USB: xhci: Support for 64-byte contexts

[deliverable/linux.git] / drivers / usb / host / xhci-ring.c

/*
 * xHCI host controller driver
 *
 * Copyright (C) 2008 Intel Corp.
 *
 * Author: Sarah Sharp
 * Some code borrowed from the Linux EHCI driver.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * Ring initialization rules:
 * 1. Each segment is initialized to zero, except for link TRBs.
 * 2. Ring cycle state = 0.  This represents Producer Cycle State (PCS) or
 *    Consumer Cycle State (CCS), depending on ring function.
 * 3. Enqueue pointer = dequeue pointer = address of first TRB in the segment.
 *
 * Ring behavior rules:
 * 1. A ring is empty if enqueue == dequeue.  This means there will always be at
 *    least one free TRB in the ring.  This is useful if you want to turn that
 *    into a link TRB and expand the ring.
 * 2. When incrementing an enqueue or dequeue pointer, if the next TRB is a
 *    link TRB, then load the pointer with the address in the link TRB.  If the
 *    link TRB had its toggle bit set, you may need to update the ring cycle
 *    state (see cycle bit rules).  You may have to do this multiple times
 *    until you reach a non-link TRB.
 * 3. A ring is full if enqueue++ (for the definition of increment above)
 *    equals the dequeue pointer.
 *
 * Cycle bit rules:
 * 1. When a consumer increments a dequeue pointer and encounters a toggle bit
 *    in a link TRB, it must toggle the ring cycle state.
 * 2. When a producer increments an enqueue pointer and encounters a toggle bit
 *    in a link TRB, it must toggle the ring cycle state.
 *
 * Producer rules:
 * 1. Check if ring is full before you enqueue.
 * 2. Write the ring cycle state to the cycle bit in the TRB you're enqueuing.
 *    Update enqueue pointer between each write (which may update the ring
 *    cycle state).
 * 3. Notify consumer.  If SW is producer, it rings the doorbell for command
 *    and endpoint rings.  If HC is the producer for the event ring,
 *    and it generates an interrupt according to interrupt modulation rules.
 *
 * Consumer rules:
 * 1. Check if TRB belongs to you.  If the cycle bit == your ring cycle state,
 *    the TRB is owned by the consumer.
 * 2. Update dequeue pointer (which may update the ring cycle state) and
 *    continue processing TRBs until you reach a TRB which is not owned by you.
 * 3. Notify the producer.  SW is the consumer for the event ring, and it
 *   updates event ring dequeue pointer.  HC is the consumer for the command and
 *   endpoint rings; it generates events on the event ring for these.
 */

#include <linux/scatterlist.h>
#include "xhci.h"

/*
 * Returns zero if the TRB isn't in this segment, otherwise it returns the DMA
 * address of the TRB.
 */
dma_addr_t xhci_trb_virt_to_dma(struct xhci_segment *seg,
                union xhci_trb *trb)
{
        unsigned long segment_offset;

        if (!seg || !trb || trb < seg->trbs)
                return 0;
        /* offset in TRBs */
        segment_offset = trb - seg->trbs;
        if (segment_offset > TRBS_PER_SEGMENT)
                return 0;
        return seg->dma + (segment_offset * sizeof(*trb));
}

/* Does this link TRB point to the first segment in a ring,
 * or was the previous TRB the last TRB on the last segment in the ERST?
 */
static inline bool last_trb_on_last_seg(struct xhci_hcd *xhci, struct xhci_ring *ring,
                struct xhci_segment *seg, union xhci_trb *trb)
{
        if (ring == xhci->event_ring)
                return (trb == &seg->trbs[TRBS_PER_SEGMENT]) &&
                        (seg->next == xhci->event_ring->first_seg);
        else
                return trb->link.control & LINK_TOGGLE;
}

/* Is this TRB a link TRB or was the last TRB the last TRB in this event ring
 * segment?  I.e. would the updated event TRB pointer step off the end of the
 * event seg?
 */
static inline int last_trb(struct xhci_hcd *xhci, struct xhci_ring *ring,
                struct xhci_segment *seg, union xhci_trb *trb)
{
        if (ring == xhci->event_ring)
                return trb == &seg->trbs[TRBS_PER_SEGMENT];
        else
                return (trb->link.control & TRB_TYPE_BITMASK) == TRB_TYPE(TRB_LINK);
}

/* Updates trb to point to the next TRB in the ring, and updates seg if the next
 * TRB is in a new segment.  This does not skip over link TRBs, and it does not
 * effect the ring dequeue or enqueue pointers.
 */
static void next_trb(struct xhci_hcd *xhci,
                struct xhci_ring *ring,
                struct xhci_segment **seg,
                union xhci_trb **trb)
{
        if (last_trb(xhci, ring, *seg, *trb)) {
                *seg = (*seg)->next;
                *trb = ((*seg)->trbs);
        } else {
                *trb = (*trb)++;
        }
}

/*
 * See Cycle bit rules. SW is the consumer for the event ring only.
 * Don't make a ring full of link TRBs.  That would be dumb and this would loop.
 */
static void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer)
{
        union xhci_trb *next = ++(ring->dequeue);
        unsigned long long addr;

        ring->deq_updates++;
        /* Update the dequeue pointer further if that was a link TRB or we're at
         * the end of an event ring segment (which doesn't have link TRBS)
         */
        while (last_trb(xhci, ring, ring->deq_seg, next)) {
                if (consumer && last_trb_on_last_seg(xhci, ring, ring->deq_seg, next)) {
                        ring->cycle_state = (ring->cycle_state ? 0 : 1);
                        if (!in_interrupt())
                                xhci_dbg(xhci, "Toggle cycle state for ring %p = %i\n",
                                                ring,
                                                (unsigned int) ring->cycle_state);
                }
                ring->deq_seg = ring->deq_seg->next;
                ring->dequeue = ring->deq_seg->trbs;
                next = ring->dequeue;
        }
        addr = (unsigned long long) xhci_trb_virt_to_dma(ring->deq_seg, ring->dequeue);
        if (ring == xhci->event_ring)
                xhci_dbg(xhci, "Event ring deq = 0x%llx (DMA)\n", addr);
        else if (ring == xhci->cmd_ring)
                xhci_dbg(xhci, "Command ring deq = 0x%llx (DMA)\n", addr);
        else
                xhci_dbg(xhci, "Ring deq = 0x%llx (DMA)\n", addr);
}

/*
 * See Cycle bit rules. SW is the consumer for the event ring only.
 * Don't make a ring full of link TRBs.  That would be dumb and this would loop.
 *
 * If we've just enqueued a TRB that is in the middle of a TD (meaning the
 * chain bit is set), then set the chain bit in all the following link TRBs.
 * If we've enqueued the last TRB in a TD, make sure the following link TRBs
 * have their chain bit cleared (so that each Link TRB is a separate TD).
 *
 * Section 6.4.4.1 of the 0.95 spec says link TRBs cannot have the chain bit
 * set, but other sections talk about dealing with the chain bit set.
 * Assume section 6.4.4.1 is wrong, and the chain bit can be set in a Link TRB.
 */
static void inc_enq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer)
{
        u32 chain;
        union xhci_trb *next;
        unsigned long long addr;

        chain = ring->enqueue->generic.field[3] & TRB_CHAIN;
        next = ++(ring->enqueue);

        ring->enq_updates++;
        /* Update the dequeue pointer further if that was a link TRB or we're at
         * the end of an event ring segment (which doesn't have link TRBS)
         */
        while (last_trb(xhci, ring, ring->enq_seg, next)) {
                if (!consumer) {
                        if (ring != xhci->event_ring) {
                                next->link.control &= ~TRB_CHAIN;
                                next->link.control |= chain;
                                /* Give this link TRB to the hardware */
                                wmb();
                                if (next->link.control & TRB_CYCLE)
                                        next->link.control &= (u32) ~TRB_CYCLE;
                                else
                                        next->link.control |= (u32) TRB_CYCLE;
                        }
                        /* Toggle the cycle bit after the last ring segment. */
                        if (last_trb_on_last_seg(xhci, ring, ring->enq_seg, next)) {
                                ring->cycle_state = (ring->cycle_state ? 0 : 1);
                                if (!in_interrupt())
                                        xhci_dbg(xhci, "Toggle cycle state for ring %p = %i\n",
                                                        ring,
                                                        (unsigned int) ring->cycle_state);
                        }
                }
                ring->enq_seg = ring->enq_seg->next;
                ring->enqueue = ring->enq_seg->trbs;
                next = ring->enqueue;
        }
        addr = (unsigned long long) xhci_trb_virt_to_dma(ring->enq_seg, ring->enqueue);
        if (ring == xhci->event_ring)
                xhci_dbg(xhci, "Event ring enq = 0x%llx (DMA)\n", addr);
        else if (ring == xhci->cmd_ring)
                xhci_dbg(xhci, "Command ring enq = 0x%llx (DMA)\n", addr);
        else
                xhci_dbg(xhci, "Ring enq = 0x%llx (DMA)\n", addr);
}

/*
 * Check to see if there's room to enqueue num_trbs on the ring.  See rules
 * above.
 * FIXME: this would be simpler and faster if we just kept track of the number
 * of free TRBs in a ring.
 */
static int room_on_ring(struct xhci_hcd *xhci, struct xhci_ring *ring,
                unsigned int num_trbs)
{
        int i;
        union xhci_trb *enq = ring->enqueue;
        struct xhci_segment *enq_seg = ring->enq_seg;

        /* Check if ring is empty */
        if (enq == ring->dequeue)
                return 1;
        /* Make sure there's an extra empty TRB available */
        for (i = 0; i <= num_trbs; ++i) {
                if (enq == ring->dequeue)
                        return 0;
                enq++;
                while (last_trb(xhci, ring, enq_seg, enq)) {
                        enq_seg = enq_seg->next;
                        enq = enq_seg->trbs;
                }
        }
        return 1;
}

void xhci_set_hc_event_deq(struct xhci_hcd *xhci)
{
        u64 temp;
        dma_addr_t deq;

        deq = xhci_trb_virt_to_dma(xhci->event_ring->deq_seg,
                        xhci->event_ring->dequeue);
        if (deq == 0 && !in_interrupt())
                xhci_warn(xhci, "WARN something wrong with SW event ring "
                                "dequeue ptr.\n");
        /* Update HC event ring dequeue pointer */
        temp = xhci_read_64(xhci, &xhci->ir_set->erst_dequeue);
        temp &= ERST_PTR_MASK;
        /* Don't clear the EHB bit (which is RW1C) because
         * there might be more events to service.
         */
        temp &= ~ERST_EHB;
        xhci_dbg(xhci, "// Write event ring dequeue pointer, preserving EHB bit\n");
        xhci_write_64(xhci, ((u64) deq & (u64) ~ERST_PTR_MASK) | temp,
                        &xhci->ir_set->erst_dequeue);
}

/* Ring the host controller doorbell after placing a command on the ring */
void xhci_ring_cmd_db(struct xhci_hcd *xhci)
{
        u32 temp;

        xhci_dbg(xhci, "// Ding dong!\n");
        temp = xhci_readl(xhci, &xhci->dba->doorbell[0]) & DB_MASK;
        xhci_writel(xhci, temp | DB_TARGET_HOST, &xhci->dba->doorbell[0]);
        /* Flush PCI posted writes */
        xhci_readl(xhci, &xhci->dba->doorbell[0]);
}

static void ring_ep_doorbell(struct xhci_hcd *xhci,
                unsigned int slot_id,
                unsigned int ep_index)
{
        struct xhci_ring *ep_ring;
        u32 field;
        __u32 __iomem *db_addr = &xhci->dba->doorbell[slot_id];

        ep_ring = xhci->devs[slot_id]->ep_rings[ep_index];
        /* Don't ring the doorbell for this endpoint if there are pending
         * cancellations because the we don't want to interrupt processing.
         */
        if (!ep_ring->cancels_pending && !(ep_ring->state & SET_DEQ_PENDING)
                        && !(ep_ring->state & EP_HALTED)) {
                field = xhci_readl(xhci, db_addr) & DB_MASK;
                xhci_writel(xhci, field | EPI_TO_DB(ep_index), db_addr);
                /* Flush PCI posted writes - FIXME Matthew Wilcox says this
                 * isn't time-critical and we shouldn't make the CPU wait for
                 * the flush.
                 */
                xhci_readl(xhci, db_addr);
        }
}

/*
 * Find the segment that trb is in.  Start searching in start_seg.
 * If we must move past a segment that has a link TRB with a toggle cycle state
 * bit set, then we will toggle the value pointed at by cycle_state.
 */
static struct xhci_segment *find_trb_seg(
                struct xhci_segment *start_seg,
                union xhci_trb  *trb, int *cycle_state)
{
        struct xhci_segment *cur_seg = start_seg;
        struct xhci_generic_trb *generic_trb;

        while (cur_seg->trbs > trb ||
                        &cur_seg->trbs[TRBS_PER_SEGMENT - 1] < trb) {
                generic_trb = &cur_seg->trbs[TRBS_PER_SEGMENT - 1].generic;
                if (TRB_TYPE(generic_trb->field[3]) == TRB_LINK &&
                                (generic_trb->field[3] & LINK_TOGGLE))
                        *cycle_state = ~(*cycle_state) & 0x1;
                cur_seg = cur_seg->next;
                if (cur_seg == start_seg)
                        /* Looped over the entire list.  Oops! */
                        return 0;
        }
        return cur_seg;
}

struct dequeue_state {
        struct xhci_segment *new_deq_seg;
        union xhci_trb *new_deq_ptr;
        int new_cycle_state;
};

/*
 * Move the xHC's endpoint ring dequeue pointer past cur_td.
 * Record the new state of the xHC's endpoint ring dequeue segment,
 * dequeue pointer, and new consumer cycle state in state.
 * Update our internal representation of the ring's dequeue pointer.
 *
 * We do this in three jumps:
 *  - First we update our new ring state to be the same as when the xHC stopped.
 *  - Then we traverse the ring to find the segment that contains
 *    the last TRB in the TD.  We toggle the xHC's new cycle state when we pass
 *    any link TRBs with the toggle cycle bit set.
 *  - Finally we move the dequeue state one TRB further, toggling the cycle bit
 *    if we've moved it past a link TRB with the toggle cycle bit set.
 */
static void find_new_dequeue_state(struct xhci_hcd *xhci,
                unsigned int slot_id, unsigned int ep_index,
                struct xhci_td *cur_td, struct dequeue_state *state)
{
        struct xhci_virt_device *dev = xhci->devs[slot_id];
        struct xhci_ring *ep_ring = dev->ep_rings[ep_index];
        struct xhci_generic_trb *trb;
        struct xhci_ep_ctx *ep_ctx;

        state->new_cycle_state = 0;
        state->new_deq_seg = find_trb_seg(cur_td->start_seg,
                        ep_ring->stopped_trb,
                        &state->new_cycle_state);
        if (!state->new_deq_seg)
                BUG();
        /* Dig out the cycle state saved by the xHC during the stop ep cmd */
        ep_ctx = xhci_get_ep_ctx(xhci, dev->out_ctx, ep_index);
        state->new_cycle_state = 0x1 & ep_ctx->deq;

        state->new_deq_ptr = cur_td->last_trb;
        state->new_deq_seg = find_trb_seg(state->new_deq_seg,
                        state->new_deq_ptr,
                        &state->new_cycle_state);
        if (!state->new_deq_seg)
                BUG();

        trb = &state->new_deq_ptr->generic;
        if (TRB_TYPE(trb->field[3]) == TRB_LINK &&
                                (trb->field[3] & LINK_TOGGLE))
                state->new_cycle_state = ~(state->new_cycle_state) & 0x1;
        next_trb(xhci, ep_ring, &state->new_deq_seg, &state->new_deq_ptr);

        /* Don't update the ring cycle state for the producer (us). */
        ep_ring->dequeue = state->new_deq_ptr;
        ep_ring->deq_seg = state->new_deq_seg;
}

static void td_to_noop(struct xhci_hcd *xhci, struct xhci_ring *ep_ring,
                struct xhci_td *cur_td)
{
        struct xhci_segment *cur_seg;
        union xhci_trb *cur_trb;

        for (cur_seg = cur_td->start_seg, cur_trb = cur_td->first_trb;
                        true;
                        next_trb(xhci, ep_ring, &cur_seg, &cur_trb)) {
                if ((cur_trb->generic.field[3] & TRB_TYPE_BITMASK) ==
                                TRB_TYPE(TRB_LINK)) {
                        /* Unchain any chained Link TRBs, but
                         * leave the pointers intact.
                         */
                        cur_trb->generic.field[3] &= ~TRB_CHAIN;
                        xhci_dbg(xhci, "Cancel (unchain) link TRB\n");
                        xhci_dbg(xhci, "Address = %p (0x%llx dma); "
                                        "in seg %p (0x%llx dma)\n",
                                        cur_trb,
                                        (unsigned long long)xhci_trb_virt_to_dma(cur_seg, cur_trb),
                                        cur_seg,
                                        (unsigned long long)cur_seg->dma);
                } else {
                        cur_trb->generic.field[0] = 0;
                        cur_trb->generic.field[1] = 0;
                        cur_trb->generic.field[2] = 0;
                        /* Preserve only the cycle bit of this TRB */
                        cur_trb->generic.field[3] &= TRB_CYCLE;
                        cur_trb->generic.field[3] |= TRB_TYPE(TRB_TR_NOOP);
                        xhci_dbg(xhci, "Cancel TRB %p (0x%llx dma) "
                                        "in seg %p (0x%llx dma)\n",
                                        cur_trb,
                                        (unsigned long long)xhci_trb_virt_to_dma(cur_seg, cur_trb),
                                        cur_seg,
                                        (unsigned long long)cur_seg->dma);
                }
                if (cur_trb == cur_td->last_trb)
                        break;
        }
}

static int queue_set_tr_deq(struct xhci_hcd *xhci, int slot_id,
                unsigned int ep_index, struct xhci_segment *deq_seg,
                union xhci_trb *deq_ptr, u32 cycle_state);

/*
 * When we get a command completion for a Stop Endpoint Command, we need to
 * unlink any cancelled TDs from the ring.  There are two ways to do that:
 *
 *  1. If the HW was in the middle of processing the TD that needs to be
 *     cancelled, then we must move the ring's dequeue pointer past the last TRB
 *     in the TD with a Set Dequeue Pointer Command.
 *  2. Otherwise, we turn all the TRBs in the TD into No-op TRBs (with the chain
 *     bit cleared) so that the HW will skip over them.
 */
static void handle_stopped_endpoint(struct xhci_hcd *xhci,
                union xhci_trb *trb)
{
        unsigned int slot_id;
        unsigned int ep_index;
        struct xhci_ring *ep_ring;
        struct list_head *entry;
        struct xhci_td *cur_td = 0;
        struct xhci_td *last_unlinked_td;

        struct dequeue_state deq_state;
#ifdef CONFIG_USB_HCD_STAT
        ktime_t stop_time = ktime_get();
#endif

        memset(&deq_state, 0, sizeof(deq_state));
        slot_id = TRB_TO_SLOT_ID(trb->generic.field[3]);
        ep_index = TRB_TO_EP_INDEX(trb->generic.field[3]);
        ep_ring = xhci->devs[slot_id]->ep_rings[ep_index];

        if (list_empty(&ep_ring->cancelled_td_list))
                return;

        /* Fix up the ep ring first, so HW stops executing cancelled TDs.
         * We have the xHCI lock, so nothing can modify this list until we drop
         * it.  We're also in the event handler, so we can't get re-interrupted
         * if another Stop Endpoint command completes
         */
        list_for_each(entry, &ep_ring->cancelled_td_list) {
                cur_td = list_entry(entry, struct xhci_td, cancelled_td_list);
                xhci_dbg(xhci, "Cancelling TD starting at %p, 0x%llx (dma).\n",
                                cur_td->first_trb,
                                (unsigned long long)xhci_trb_virt_to_dma(cur_td->start_seg, cur_td->first_trb));
                /*
                 * If we stopped on the TD we need to cancel, then we have to
                 * move the xHC endpoint ring dequeue pointer past this TD.
                 */
                if (cur_td == ep_ring->stopped_td)
                        find_new_dequeue_state(xhci, slot_id, ep_index, cur_td,
                                        &deq_state);
                else
                        td_to_noop(xhci, ep_ring, cur_td);
                /*
                 * The event handler won't see a completion for this TD anymore,
                 * so remove it from the endpoint ring's TD list.  Keep it in
                 * the cancelled TD list for URB completion later.
                 */
                list_del(&cur_td->td_list);
                ep_ring->cancels_pending--;
        }
        last_unlinked_td = cur_td;

        /* If necessary, queue a Set Transfer Ring Dequeue Pointer command */
        if (deq_state.new_deq_ptr && deq_state.new_deq_seg) {
                xhci_dbg(xhci, "Set TR Deq Ptr cmd, new deq seg = %p (0x%llx dma), "
                                "new deq ptr = %p (0x%llx dma), new cycle = %u\n",
                                deq_state.new_deq_seg,
                                (unsigned long long)deq_state.new_deq_seg->dma,
                                deq_state.new_deq_ptr,
                                (unsigned long long)xhci_trb_virt_to_dma(deq_state.new_deq_seg, deq_state.new_deq_ptr),
                                deq_state.new_cycle_state);
                queue_set_tr_deq(xhci, slot_id, ep_index,
                                deq_state.new_deq_seg,
                                deq_state.new_deq_ptr,
                                (u32) deq_state.new_cycle_state);
                /* Stop the TD queueing code from ringing the doorbell until
                 * this command completes.  The HC won't set the dequeue pointer
                 * if the ring is running, and ringing the doorbell starts the
                 * ring running.
                 */
                ep_ring->state |= SET_DEQ_PENDING;
                xhci_ring_cmd_db(xhci);
        } else {
                /* Otherwise just ring the doorbell to restart the ring */
                ring_ep_doorbell(xhci, slot_id, ep_index);
        }

        /*
         * Drop the lock and complete the URBs in the cancelled TD list.
         * New TDs to be cancelled might be added to the end of the list before
         * we can complete all the URBs for the TDs we already unlinked.
         * So stop when we've completed the URB for the last TD we unlinked.
         */
        do {
                cur_td = list_entry(ep_ring->cancelled_td_list.next,
                                struct xhci_td, cancelled_td_list);
                list_del(&cur_td->cancelled_td_list);

                /* Clean up the cancelled URB */
#ifdef CONFIG_USB_HCD_STAT
                hcd_stat_update(xhci->tp_stat, cur_td->urb->actual_length,
                                ktime_sub(stop_time, cur_td->start_time));
#endif
                cur_td->urb->hcpriv = NULL;
                usb_hcd_unlink_urb_from_ep(xhci_to_hcd(xhci), cur_td->urb);

                xhci_dbg(xhci, "Giveback cancelled URB %p\n", cur_td->urb);
                spin_unlock(&xhci->lock);
                /* Doesn't matter what we pass for status, since the core will
                 * just overwrite it (because the URB has been unlinked).
                 */
                usb_hcd_giveback_urb(xhci_to_hcd(xhci), cur_td->urb, 0);
                kfree(cur_td);

                spin_lock(&xhci->lock);
        } while (cur_td != last_unlinked_td);

        /* Return to the event handler with xhci->lock re-acquired */
}

/*
 * When we get a completion for a Set Transfer Ring Dequeue Pointer command,
 * we need to clear the set deq pending flag in the endpoint ring state, so that
 * the TD queueing code can ring the doorbell again.  We also need to ring the
 * endpoint doorbell to restart the ring, but only if there aren't more
 * cancellations pending.
 */
static void handle_set_deq_completion(struct xhci_hcd *xhci,
                struct xhci_event_cmd *event,
                union xhci_trb *trb)
{
        unsigned int slot_id;
        unsigned int ep_index;
        struct xhci_ring *ep_ring;
        struct xhci_virt_device *dev;
        struct xhci_ep_ctx *ep_ctx;
        struct xhci_slot_ctx *slot_ctx;

        slot_id = TRB_TO_SLOT_ID(trb->generic.field[3]);
        ep_index = TRB_TO_EP_INDEX(trb->generic.field[3]);
        dev = xhci->devs[slot_id];
        ep_ring = dev->ep_rings[ep_index];
        ep_ctx = xhci_get_ep_ctx(xhci, dev->out_ctx, ep_index);
        slot_ctx = xhci_get_slot_ctx(xhci, dev->out_ctx);

        if (GET_COMP_CODE(event->status) != COMP_SUCCESS) {
                unsigned int ep_state;
                unsigned int slot_state;

                switch (GET_COMP_CODE(event->status)) {
                case COMP_TRB_ERR:
                        xhci_warn(xhci, "WARN Set TR Deq Ptr cmd invalid because "
                                        "of stream ID configuration\n");
                        break;
                case COMP_CTX_STATE:
                        xhci_warn(xhci, "WARN Set TR Deq Ptr cmd failed due "
                                        "to incorrect slot or ep state.\n");
                        ep_state = ep_ctx->ep_info;
                        ep_state &= EP_STATE_MASK;
                        slot_state = slot_ctx->dev_state;
                        slot_state = GET_SLOT_STATE(slot_state);
                        xhci_dbg(xhci, "Slot state = %u, EP state = %u\n",
                                        slot_state, ep_state);
                        break;
                case COMP_EBADSLT:
                        xhci_warn(xhci, "WARN Set TR Deq Ptr cmd failed because "
                                        "slot %u was not enabled.\n", slot_id);
                        break;
                default:
                        xhci_warn(xhci, "WARN Set TR Deq Ptr cmd with unknown "
                                        "completion code of %u.\n",
                                        GET_COMP_CODE(event->status));
                        break;
                }
                /* OK what do we do now?  The endpoint state is hosed, and we
                 * should never get to this point if the synchronization between
                 * queueing, and endpoint state are correct.  This might happen
                 * if the device gets disconnected after we've finished
                 * cancelling URBs, which might not be an error...
                 */
        } else {
                xhci_dbg(xhci, "Successful Set TR Deq Ptr cmd, deq = @%08llx\n",
                                ep_ctx->deq);
        }

        ep_ring->state &= ~SET_DEQ_PENDING;
        ring_ep_doorbell(xhci, slot_id, ep_index);
}

static void handle_reset_ep_completion(struct xhci_hcd *xhci,
                struct xhci_event_cmd *event,
                union xhci_trb *trb)
{
        int slot_id;
        unsigned int ep_index;

        slot_id = TRB_TO_SLOT_ID(trb->generic.field[3]);
        ep_index = TRB_TO_EP_INDEX(trb->generic.field[3]);
        /* This command will only fail if the endpoint wasn't halted,
         * but we don't care.
         */
        xhci_dbg(xhci, "Ignoring reset ep completion code of %u\n",
                        (unsigned int) GET_COMP_CODE(event->status));

        /* Clear our internal halted state and restart the ring */
        xhci->devs[slot_id]->ep_rings[ep_index]->state &= ~EP_HALTED;
        ring_ep_doorbell(xhci, slot_id, ep_index);
}

static void handle_cmd_completion(struct xhci_hcd *xhci,
                struct xhci_event_cmd *event)
{
        int slot_id = TRB_TO_SLOT_ID(event->flags);
        u64 cmd_dma;
        dma_addr_t cmd_dequeue_dma;

        cmd_dma = event->cmd_trb;
        cmd_dequeue_dma = xhci_trb_virt_to_dma(xhci->cmd_ring->deq_seg,
                        xhci->cmd_ring->dequeue);
        /* Is the command ring deq ptr out of sync with the deq seg ptr? */
        if (cmd_dequeue_dma == 0) {
                xhci->error_bitmask |= 1 << 4;
                return;
        }
        /* Does the DMA address match our internal dequeue pointer address? */
        if (cmd_dma != (u64) cmd_dequeue_dma) {
                xhci->error_bitmask |= 1 << 5;
                return;
        }
        switch (xhci->cmd_ring->dequeue->generic.field[3] & TRB_TYPE_BITMASK) {
        case TRB_TYPE(TRB_ENABLE_SLOT):
                if (GET_COMP_CODE(event->status) == COMP_SUCCESS)
                        xhci->slot_id = slot_id;
                else
                        xhci->slot_id = 0;
                complete(&xhci->addr_dev);
                break;
        case TRB_TYPE(TRB_DISABLE_SLOT):
                if (xhci->devs[slot_id])
                        xhci_free_virt_device(xhci, slot_id);
                break;
        case TRB_TYPE(TRB_CONFIG_EP):
                xhci->devs[slot_id]->cmd_status = GET_COMP_CODE(event->status);
                complete(&xhci->devs[slot_id]->cmd_completion);
                break;
        case TRB_TYPE(TRB_ADDR_DEV):
                xhci->devs[slot_id]->cmd_status = GET_COMP_CODE(event->status);
                complete(&xhci->addr_dev);
                break;
        case TRB_TYPE(TRB_STOP_RING):
                handle_stopped_endpoint(xhci, xhci->cmd_ring->dequeue);
                break;
        case TRB_TYPE(TRB_SET_DEQ):
                handle_set_deq_completion(xhci, event, xhci->cmd_ring->dequeue);
                break;
        case TRB_TYPE(TRB_CMD_NOOP):
                ++xhci->noops_handled;
                break;
        case TRB_TYPE(TRB_RESET_EP):
                handle_reset_ep_completion(xhci, event, xhci->cmd_ring->dequeue);
                break;
        default:
                /* Skip over unknown commands on the event ring */
                xhci->error_bitmask |= 1 << 6;
                break;
        }
        inc_deq(xhci, xhci->cmd_ring, false);
}

static void handle_port_status(struct xhci_hcd *xhci,
                union xhci_trb *event)
{
        u32 port_id;

        /* Port status change events always have a successful completion code */
        if (GET_COMP_CODE(event->generic.field[2]) != COMP_SUCCESS) {
                xhci_warn(xhci, "WARN: xHC returned failed port status event\n");
                xhci->error_bitmask |= 1 << 8;
        }
        /* FIXME: core doesn't care about all port link state changes yet */
        port_id = GET_PORT_ID(event->generic.field[0]);
        xhci_dbg(xhci, "Port Status Change Event for port %d\n", port_id);

        /* Update event ring dequeue pointer before dropping the lock */
        inc_deq(xhci, xhci->event_ring, true);
        xhci_set_hc_event_deq(xhci);

        spin_unlock(&xhci->lock);
        /* Pass this up to the core */
        usb_hcd_poll_rh_status(xhci_to_hcd(xhci));
        spin_lock(&xhci->lock);
}

/*
 * This TD is defined by the TRBs starting at start_trb in start_seg and ending
 * at end_trb, which may be in another segment.  If the suspect DMA address is a
 * TRB in this TD, this function returns that TRB's segment.  Otherwise it
 * returns 0.
 */
static struct xhci_segment *trb_in_td(
                struct xhci_segment *start_seg,
                union xhci_trb  *start_trb,
                union xhci_trb  *end_trb,
                dma_addr_t      suspect_dma)
{
        dma_addr_t start_dma;
        dma_addr_t end_seg_dma;
        dma_addr_t end_trb_dma;
        struct xhci_segment *cur_seg;

        start_dma = xhci_trb_virt_to_dma(start_seg, start_trb);
        cur_seg = start_seg;

        do {
                /* We may get an event for a Link TRB in the middle of a TD */
                end_seg_dma = xhci_trb_virt_to_dma(cur_seg,
                                &start_seg->trbs[TRBS_PER_SEGMENT - 1]);
                /* If the end TRB isn't in this segment, this is set to 0 */
                end_trb_dma = xhci_trb_virt_to_dma(cur_seg, end_trb);

                if (end_trb_dma > 0) {
                        /* The end TRB is in this segment, so suspect should be here */
                        if (start_dma <= end_trb_dma) {
                                if (suspect_dma >= start_dma && suspect_dma <= end_trb_dma)
                                        return cur_seg;
                        } else {
                                /* Case for one segment with
                                 * a TD wrapped around to the top
                                 */
                                if ((suspect_dma >= start_dma &&
                                                        suspect_dma <= end_seg_dma) ||
                                                (suspect_dma >= cur_seg->dma &&
                                                 suspect_dma <= end_trb_dma))
                                        return cur_seg;
                        }
                        return 0;
                } else {
                        /* Might still be somewhere in this segment */
                        if (suspect_dma >= start_dma && suspect_dma <= end_seg_dma)
                                return cur_seg;
                }
                cur_seg = cur_seg->next;
                start_dma = xhci_trb_virt_to_dma(cur_seg, &cur_seg->trbs[0]);
        } while (1);

}

/*
 * If this function returns an error condition, it means it got a Transfer
 * event with a corrupted Slot ID, Endpoint ID, or TRB DMA address.
 * At this point, the host controller is probably hosed and should be reset.
 */
static int handle_tx_event(struct xhci_hcd *xhci,
                struct xhci_transfer_event *event)
{
        struct xhci_virt_device *xdev;
        struct xhci_ring *ep_ring;
        int ep_index;
        struct xhci_td *td = 0;
        dma_addr_t event_dma;
        struct xhci_segment *event_seg;
        union xhci_trb *event_trb;
        struct urb *urb = 0;
        int status = -EINPROGRESS;
        struct xhci_ep_ctx *ep_ctx;

        xhci_dbg(xhci, "In %s\n", __func__);
        xdev = xhci->devs[TRB_TO_SLOT_ID(event->flags)];
        if (!xdev) {
                xhci_err(xhci, "ERROR Transfer event pointed to bad slot\n");
                return -ENODEV;
        }

        /* Endpoint ID is 1 based, our index is zero based */
        ep_index = TRB_TO_EP_ID(event->flags) - 1;
        xhci_dbg(xhci, "%s - ep index = %d\n", __func__, ep_index);
        ep_ring = xdev->ep_rings[ep_index];
        ep_ctx = xhci_get_ep_ctx(xhci, xdev->out_ctx, ep_index);
        if (!ep_ring || (ep_ctx->ep_info & EP_STATE_MASK) == EP_STATE_DISABLED) {
                xhci_err(xhci, "ERROR Transfer event pointed to disabled endpoint\n");
                return -ENODEV;
        }

        event_dma = event->buffer;
        /* This TRB should be in the TD at the head of this ring's TD list */
        xhci_dbg(xhci, "%s - checking for list empty\n", __func__);
        if (list_empty(&ep_ring->td_list)) {
                xhci_warn(xhci, "WARN Event TRB for slot %d ep %d with no TDs queued?\n",
                                TRB_TO_SLOT_ID(event->flags), ep_index);
                xhci_dbg(xhci, "Event TRB with TRB type ID %u\n",
                                (unsigned int) (event->flags & TRB_TYPE_BITMASK)>>10);
                xhci_print_trb_offsets(xhci, (union xhci_trb *) event);
                urb = NULL;
                goto cleanup;
        }
        xhci_dbg(xhci, "%s - getting list entry\n", __func__);
        td = list_entry(ep_ring->td_list.next, struct xhci_td, td_list);

        /* Is this a TRB in the currently executing TD? */
        xhci_dbg(xhci, "%s - looking for TD\n", __func__);
        event_seg = trb_in_td(ep_ring->deq_seg, ep_ring->dequeue,
                        td->last_trb, event_dma);
        xhci_dbg(xhci, "%s - found event_seg = %p\n", __func__, event_seg);
        if (!event_seg) {
                /* HC is busted, give up! */
                xhci_err(xhci, "ERROR Transfer event TRB DMA ptr not part of current TD\n");
                return -ESHUTDOWN;
        }
        event_trb = &event_seg->trbs[(event_dma - event_seg->dma) / sizeof(*event_trb)];
        xhci_dbg(xhci, "Event TRB with TRB type ID %u\n",
                        (unsigned int) (event->flags & TRB_TYPE_BITMASK)>>10);
        xhci_dbg(xhci, "Offset 0x00 (buffer lo) = 0x%x\n",
                        lower_32_bits(event->buffer));
        xhci_dbg(xhci, "Offset 0x04 (buffer hi) = 0x%x\n",
                        upper_32_bits(event->buffer));
        xhci_dbg(xhci, "Offset 0x08 (transfer length) = 0x%x\n",
                        (unsigned int) event->transfer_len);
        xhci_dbg(xhci, "Offset 0x0C (flags) = 0x%x\n",
                        (unsigned int) event->flags);

        /* Look for common error cases */
        switch (GET_COMP_CODE(event->transfer_len)) {
        /* Skip codes that require special handling depending on
         * transfer type
         */
        case COMP_SUCCESS:
        case COMP_SHORT_TX:
                break;
        case COMP_STOP:
                xhci_dbg(xhci, "Stopped on Transfer TRB\n");
                break;
        case COMP_STOP_INVAL:
                xhci_dbg(xhci, "Stopped on No-op or Link TRB\n");
                break;
        case COMP_STALL:
                xhci_warn(xhci, "WARN: Stalled endpoint\n");
                ep_ring->state |= EP_HALTED;
                status = -EPIPE;
                break;
        case COMP_TRB_ERR:
                xhci_warn(xhci, "WARN: TRB error on endpoint\n");
                status = -EILSEQ;
                break;
        case COMP_TX_ERR:
                xhci_warn(xhci, "WARN: transfer error on endpoint\n");
                status = -EPROTO;
                break;
        case COMP_BABBLE:
                xhci_warn(xhci, "WARN: babble error on endpoint\n");
                status = -EOVERFLOW;
                break;
        case COMP_DB_ERR:
                xhci_warn(xhci, "WARN: HC couldn't access mem fast enough\n");
                status = -ENOSR;
                break;
        default:
                xhci_warn(xhci, "ERROR Unknown event condition, HC probably busted\n");
                urb = NULL;
                goto cleanup;
        }
        /* Now update the urb's actual_length and give back to the core */
        /* Was this a control transfer? */
        if (usb_endpoint_xfer_control(&td->urb->ep->desc)) {
                xhci_debug_trb(xhci, xhci->event_ring->dequeue);
                switch (GET_COMP_CODE(event->transfer_len)) {
                case COMP_SUCCESS:
                        if (event_trb == ep_ring->dequeue) {
                                xhci_warn(xhci, "WARN: Success on ctrl setup TRB without IOC set??\n");
                                status = -ESHUTDOWN;
                        } else if (event_trb != td->last_trb) {
                                xhci_warn(xhci, "WARN: Success on ctrl data TRB without IOC set??\n");
                                status = -ESHUTDOWN;
                        } else {
                                xhci_dbg(xhci, "Successful control transfer!\n");
                                status = 0;
                        }
                        break;
                case COMP_SHORT_TX:
                        xhci_warn(xhci, "WARN: short transfer on control ep\n");
                        status = -EREMOTEIO;
                        break;
                default:
                        /* Others already handled above */
                        break;
                }
                /*
                 * Did we transfer any data, despite the errors that might have
                 * happened?  I.e. did we get past the setup stage?
                 */
                if (event_trb != ep_ring->dequeue) {
                        /* The event was for the status stage */
                        if (event_trb == td->last_trb) {
                                /* Did we already see a short data stage? */
                                if (td->urb->actual_length != 0)
                                        status = -EREMOTEIO;
                                else
                                        td->urb->actual_length =
                                                td->urb->transfer_buffer_length;
                        } else {
                        /* Maybe the event was for the data stage? */
                                if (GET_COMP_CODE(event->transfer_len) != COMP_STOP_INVAL) {
                                        /* We didn't stop on a link TRB in the middle */
                                        td->urb->actual_length =
                                                td->urb->transfer_buffer_length -
                                                TRB_LEN(event->transfer_len);
                                        xhci_dbg(xhci, "Waiting for status stage event\n");
                                        urb = NULL;
                                        goto cleanup;
                                }
                        }
                }
        } else {
                switch (GET_COMP_CODE(event->transfer_len)) {
                case COMP_SUCCESS:
                        /* Double check that the HW transferred everything. */
                        if (event_trb != td->last_trb) {
                                xhci_warn(xhci, "WARN Successful completion "
                                                "on short TX\n");
                                if (td->urb->transfer_flags & URB_SHORT_NOT_OK)
                                        status = -EREMOTEIO;
                                else
                                        status = 0;
                        } else {
                                xhci_dbg(xhci, "Successful bulk transfer!\n");
                                status = 0;
                        }
                        break;
                case COMP_SHORT_TX:
                        if (td->urb->transfer_flags & URB_SHORT_NOT_OK)
                                status = -EREMOTEIO;
                        else
                                status = 0;
                        break;
                default:
                        /* Others already handled above */
                        break;
                }
                dev_dbg(&td->urb->dev->dev,
                                "ep %#x - asked for %d bytes, "
                                "%d bytes untransferred\n",
                                td->urb->ep->desc.bEndpointAddress,
                                td->urb->transfer_buffer_length,
                                TRB_LEN(event->transfer_len));
                /* Fast path - was this the last TRB in the TD for this URB? */
                if (event_trb == td->last_trb) {
                        if (TRB_LEN(event->transfer_len) != 0) {
                                td->urb->actual_length =
                                        td->urb->transfer_buffer_length -
                                        TRB_LEN(event->transfer_len);
                                if (td->urb->actual_length < 0) {
                                        xhci_warn(xhci, "HC gave bad length "
                                                        "of %d bytes left\n",
                                                        TRB_LEN(event->transfer_len));
                                        td->urb->actual_length = 0;
                                }
                                if (td->urb->transfer_flags & URB_SHORT_NOT_OK)
                                        status = -EREMOTEIO;
                                else
                                        status = 0;
                        } else {
                                td->urb->actual_length = td->urb->transfer_buffer_length;
                                /* Ignore a short packet completion if the
                                 * untransferred length was zero.
                                 */
                                status = 0;
                        }
                } else {
                        /* Slow path - walk the list, starting from the dequeue
                         * pointer, to get the actual length transferred.
                         */
                        union xhci_trb *cur_trb;
                        struct xhci_segment *cur_seg;

                        td->urb->actual_length = 0;
                        for (cur_trb = ep_ring->dequeue, cur_seg = ep_ring->deq_seg;
                                        cur_trb != event_trb;
                                        next_trb(xhci, ep_ring, &cur_seg, &cur_trb)) {
                                if (TRB_TYPE(cur_trb->generic.field[3]) != TRB_TR_NOOP &&
                                                TRB_TYPE(cur_trb->generic.field[3]) != TRB_LINK)
                                        td->urb->actual_length +=
                                                TRB_LEN(cur_trb->generic.field[2]);
                        }
                        /* If the ring didn't stop on a Link or No-op TRB, add
                         * in the actual bytes transferred from the Normal TRB
                         */
                        if (GET_COMP_CODE(event->transfer_len) != COMP_STOP_INVAL)
                                td->urb->actual_length +=
                                        TRB_LEN(cur_trb->generic.field[2]) -
                                        TRB_LEN(event->transfer_len);
                }
        }
        /* The Endpoint Stop Command completion will take care of
         * any stopped TDs.  A stopped TD may be restarted, so don't update the
         * ring dequeue pointer or take this TD off any lists yet.
         */
        if (GET_COMP_CODE(event->transfer_len) == COMP_STOP_INVAL ||
                        GET_COMP_CODE(event->transfer_len) == COMP_STOP) {
                ep_ring->stopped_td = td;
                ep_ring->stopped_trb = event_trb;
        } else {
                /* Update ring dequeue pointer */
                while (ep_ring->dequeue != td->last_trb)
                        inc_deq(xhci, ep_ring, false);
                inc_deq(xhci, ep_ring, false);

                /* Clean up the endpoint's TD list */
                urb = td->urb;
                list_del(&td->td_list);
                /* Was this TD slated to be cancelled but completed anyway? */
                if (!list_empty(&td->cancelled_td_list)) {
                        list_del(&td->cancelled_td_list);
                        ep_ring->cancels_pending--;
                }
                kfree(td);
                urb->hcpriv = NULL;
        }
cleanup:
        inc_deq(xhci, xhci->event_ring, true);
        xhci_set_hc_event_deq(xhci);

        /* FIXME for multi-TD URBs (who have buffers bigger than 64MB) */
        if (urb) {
                usb_hcd_unlink_urb_from_ep(xhci_to_hcd(xhci), urb);
                xhci_dbg(xhci, "Giveback URB %p, len = %d, status = %d\n",
                                urb, td->urb->actual_length, status);
                spin_unlock(&xhci->lock);
                usb_hcd_giveback_urb(xhci_to_hcd(xhci), urb, status);
                spin_lock(&xhci->lock);
        }
        return 0;
}

/*
 * This function handles all OS-owned events on the event ring.  It may drop
 * xhci->lock between event processing (e.g. to pass up port status changes).
 */
void xhci_handle_event(struct xhci_hcd *xhci)
{
        union xhci_trb *event;
        int update_ptrs = 1;
        int ret;

        xhci_dbg(xhci, "In %s\n", __func__);
        if (!xhci->event_ring || !xhci->event_ring->dequeue) {
                xhci->error_bitmask |= 1 << 1;
                return;
        }

        event = xhci->event_ring->dequeue;
        /* Does the HC or OS own the TRB? */
        if ((event->event_cmd.flags & TRB_CYCLE) !=
                        xhci->event_ring->cycle_state) {
                xhci->error_bitmask |= 1 << 2;
                return;
        }
        xhci_dbg(xhci, "%s - OS owns TRB\n", __func__);

        /* FIXME: Handle more event types. */
        switch ((event->event_cmd.flags & TRB_TYPE_BITMASK)) {
        case TRB_TYPE(TRB_COMPLETION):
                xhci_dbg(xhci, "%s - calling handle_cmd_completion\n", __func__);
                handle_cmd_completion(xhci, &event->event_cmd);
                xhci_dbg(xhci, "%s - returned from handle_cmd_completion\n", __func__);
                break;
        case TRB_TYPE(TRB_PORT_STATUS):
                xhci_dbg(xhci, "%s - calling handle_port_status\n", __func__);
                handle_port_status(xhci, event);
                xhci_dbg(xhci, "%s - returned from handle_port_status\n", __func__);
                update_ptrs = 0;
                break;
        case TRB_TYPE(TRB_TRANSFER):
                xhci_dbg(xhci, "%s - calling handle_tx_event\n", __func__);
                ret = handle_tx_event(xhci, &event->trans_event);
                xhci_dbg(xhci, "%s - returned from handle_tx_event\n", __func__);
                if (ret < 0)
                        xhci->error_bitmask |= 1 << 9;
                else
                        update_ptrs = 0;
                break;
        default:
                xhci->error_bitmask |= 1 << 3;
        }

        if (update_ptrs) {
                /* Update SW and HC event ring dequeue pointer */
                inc_deq(xhci, xhci->event_ring, true);
                xhci_set_hc_event_deq(xhci);
        }
        /* Are there more items on the event ring? */
        xhci_handle_event(xhci);
}

/****           Endpoint Ring Operations        ****/

/*
 * Generic function for queueing a TRB on a ring.
 * The caller must have checked to make sure there's room on the ring.
 */
static void queue_trb(struct xhci_hcd *xhci, struct xhci_ring *ring,
                bool consumer,
                u32 field1, u32 field2, u32 field3, u32 field4)
{
        struct xhci_generic_trb *trb;

        trb = &ring->enqueue->generic;
        trb->field[0] = field1;
        trb->field[1] = field2;
        trb->field[2] = field3;
        trb->field[3] = field4;
        inc_enq(xhci, ring, consumer);
}

/*
 * Does various checks on the endpoint ring, and makes it ready to queue num_trbs.
 * FIXME allocate segments if the ring is full.
 */
static int prepare_ring(struct xhci_hcd *xhci, struct xhci_ring *ep_ring,
                u32 ep_state, unsigned int num_trbs, gfp_t mem_flags)
{
        /* Make sure the endpoint has been added to xHC schedule */
        xhci_dbg(xhci, "Endpoint state = 0x%x\n", ep_state);
        switch (ep_state) {
        case EP_STATE_DISABLED:
                /*
                 * USB core changed config/interfaces without notifying us,
                 * or hardware is reporting the wrong state.
                 */
                xhci_warn(xhci, "WARN urb submitted to disabled ep\n");
                return -ENOENT;
        case EP_STATE_HALTED:
        case EP_STATE_ERROR:
                xhci_warn(xhci, "WARN waiting for halt or error on ep "
                                "to be cleared\n");
                /* FIXME event handling code for error needs to clear it */
                /* XXX not sure if this should be -ENOENT or not */
                return -EINVAL;
        case EP_STATE_STOPPED:
        case EP_STATE_RUNNING:
                break;
        default:
                xhci_err(xhci, "ERROR unknown endpoint state for ep\n");
                /*
                 * FIXME issue Configure Endpoint command to try to get the HC
                 * back into a known state.
                 */
                return -EINVAL;
        }
        if (!room_on_ring(xhci, ep_ring, num_trbs)) {
                /* FIXME allocate more room */
                xhci_err(xhci, "ERROR no room on ep ring\n");
                return -ENOMEM;
        }
        return 0;
}

static int prepare_transfer(struct xhci_hcd *xhci,
                struct xhci_virt_device *xdev,
                unsigned int ep_index,
                unsigned int num_trbs,
                struct urb *urb,
                struct xhci_td **td,
                gfp_t mem_flags)
{
        int ret;
        struct xhci_ep_ctx *ep_ctx = xhci_get_ep_ctx(xhci, xdev->out_ctx, ep_index);
        ret = prepare_ring(xhci, xdev->ep_rings[ep_index],
                        ep_ctx->ep_info & EP_STATE_MASK,
                        num_trbs, mem_flags);
        if (ret)
                return ret;
        *td = kzalloc(sizeof(struct xhci_td), mem_flags);
        if (!*td)
                return -ENOMEM;
        INIT_LIST_HEAD(&(*td)->td_list);
        INIT_LIST_HEAD(&(*td)->cancelled_td_list);

        ret = usb_hcd_link_urb_to_ep(xhci_to_hcd(xhci), urb);
        if (unlikely(ret)) {
                kfree(*td);
                return ret;
        }

        (*td)->urb = urb;
        urb->hcpriv = (void *) (*td);
        /* Add this TD to the tail of the endpoint ring's TD list */
        list_add_tail(&(*td)->td_list, &xdev->ep_rings[ep_index]->td_list);
        (*td)->start_seg = xdev->ep_rings[ep_index]->enq_seg;
        (*td)->first_trb = xdev->ep_rings[ep_index]->enqueue;

        return 0;
}

static unsigned int count_sg_trbs_needed(struct xhci_hcd *xhci, struct urb *urb)
{
        int num_sgs, num_trbs, running_total, temp, i;
        struct scatterlist *sg;

        sg = NULL;
        num_sgs = urb->num_sgs;
        temp = urb->transfer_buffer_length;

        xhci_dbg(xhci, "count sg list trbs: \n");
        num_trbs = 0;
        for_each_sg(urb->sg->sg, sg, num_sgs, i) {
                unsigned int previous_total_trbs = num_trbs;
                unsigned int len = sg_dma_len(sg);

                /* Scatter gather list entries may cross 64KB boundaries */
                running_total = TRB_MAX_BUFF_SIZE -
                        (sg_dma_address(sg) & ((1 << TRB_MAX_BUFF_SHIFT) - 1));
                if (running_total != 0)
                        num_trbs++;

                /* How many more 64KB chunks to transfer, how many more TRBs? */
                while (running_total < sg_dma_len(sg)) {
                        num_trbs++;
                        running_total += TRB_MAX_BUFF_SIZE;
                }
                xhci_dbg(xhci, " sg #%d: dma = %#llx, len = %#x (%d), num_trbs = %d\n",
                                i, (unsigned long long)sg_dma_address(sg),
                                len, len, num_trbs - previous_total_trbs);

                len = min_t(int, len, temp);
                temp -= len;
                if (temp == 0)
                        break;
        }
        xhci_dbg(xhci, "\n");
        if (!in_interrupt())
                dev_dbg(&urb->dev->dev, "ep %#x - urb len = %d, sglist used, num_trbs = %d\n",
                                urb->ep->desc.bEndpointAddress,
                                urb->transfer_buffer_length,
                                num_trbs);
        return num_trbs;
}

static void check_trb_math(struct urb *urb, int num_trbs, int running_total)
{
        if (num_trbs != 0)
                dev_dbg(&urb->dev->dev, "%s - ep %#x - Miscalculated number of "
                                "TRBs, %d left\n", __func__,
                                urb->ep->desc.bEndpointAddress, num_trbs);
        if (running_total != urb->transfer_buffer_length)
                dev_dbg(&urb->dev->dev, "%s - ep %#x - Miscalculated tx length, "
                                "queued %#x (%d), asked for %#x (%d)\n",
                                __func__,
                                urb->ep->desc.bEndpointAddress,
                                running_total, running_total,
                                urb->transfer_buffer_length,
                                urb->transfer_buffer_length);
}

static void giveback_first_trb(struct xhci_hcd *xhci, int slot_id,
                unsigned int ep_index, int start_cycle,
                struct xhci_generic_trb *start_trb, struct xhci_td *td)
{
        /*
         * Pass all the TRBs to the hardware at once and make sure this write
         * isn't reordered.
         */
        wmb();
        start_trb->field[3] |= start_cycle;
        ring_ep_doorbell(xhci, slot_id, ep_index);
}

static int queue_bulk_sg_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
                struct urb *urb, int slot_id, unsigned int ep_index)
{
        struct xhci_ring *ep_ring;
        unsigned int num_trbs;
        struct xhci_td *td;
        struct scatterlist *sg;
        int num_sgs;
        int trb_buff_len, this_sg_len, running_total;
        bool first_trb;
        u64 addr;

        struct xhci_generic_trb *start_trb;
        int start_cycle;

        ep_ring = xhci->devs[slot_id]->ep_rings[ep_index];
        num_trbs = count_sg_trbs_needed(xhci, urb);
        num_sgs = urb->num_sgs;

        trb_buff_len = prepare_transfer(xhci, xhci->devs[slot_id],
                        ep_index, num_trbs, urb, &td, mem_flags);
        if (trb_buff_len < 0)
                return trb_buff_len;
        /*
         * Don't give the first TRB to the hardware (by toggling the cycle bit)
         * until we've finished creating all the other TRBs.  The ring's cycle
         * state may change as we enqueue the other TRBs, so save it too.
         */
        start_trb = &ep_ring->enqueue->generic;
        start_cycle = ep_ring->cycle_state;

        running_total = 0;
        /*
         * How much data is in the first TRB?
         *
         * There are three forces at work for TRB buffer pointers and lengths:
         * 1. We don't want to walk off the end of this sg-list entry buffer.
         * 2. The transfer length that the driver requested may be smaller than
         *    the amount of memory allocated for this scatter-gather list.
         * 3. TRBs buffers can't cross 64KB boundaries.
         */
        sg = urb->sg->sg;
        addr = (u64) sg_dma_address(sg);
        this_sg_len = sg_dma_len(sg);
        trb_buff_len = TRB_MAX_BUFF_SIZE -
                (addr & ((1 << TRB_MAX_BUFF_SHIFT) - 1));
        trb_buff_len = min_t(int, trb_buff_len, this_sg_len);
        if (trb_buff_len > urb->transfer_buffer_length)
                trb_buff_len = urb->transfer_buffer_length;
        xhci_dbg(xhci, "First length to xfer from 1st sglist entry = %u\n",
                        trb_buff_len);

        first_trb = true;
        /* Queue the first TRB, even if it's zero-length */
        do {
                u32 field = 0;
                u32 length_field = 0;

                /* Don't change the cycle bit of the first TRB until later */
                if (first_trb)
                        first_trb = false;
                else
                        field |= ep_ring->cycle_state;

                /* Chain all the TRBs together; clear the chain bit in the last
                 * TRB to indicate it's the last TRB in the chain.
                 */
                if (num_trbs > 1) {
                        field |= TRB_CHAIN;
                } else {
                        /* FIXME - add check for ZERO_PACKET flag before this */
                        td->last_trb = ep_ring->enqueue;
                        field |= TRB_IOC;
                }
                xhci_dbg(xhci, " sg entry: dma = %#x, len = %#x (%d), "
                                "64KB boundary at %#x, end dma = %#x\n",
                                (unsigned int) addr, trb_buff_len, trb_buff_len,
                                (unsigned int) (addr + TRB_MAX_BUFF_SIZE) & ~(TRB_MAX_BUFF_SIZE - 1),
                                (unsigned int) addr + trb_buff_len);
                if (TRB_MAX_BUFF_SIZE -
                                (addr & ((1 << TRB_MAX_BUFF_SHIFT) - 1)) < trb_buff_len) {
                        xhci_warn(xhci, "WARN: sg dma xfer crosses 64KB boundaries!\n");
                        xhci_dbg(xhci, "Next boundary at %#x, end dma = %#x\n",
                                        (unsigned int) (addr + TRB_MAX_BUFF_SIZE) & ~(TRB_MAX_BUFF_SIZE - 1),
                                        (unsigned int) addr + trb_buff_len);
                }
                length_field = TRB_LEN(trb_buff_len) |
                        TD_REMAINDER(urb->transfer_buffer_length - running_total) |
                        TRB_INTR_TARGET(0);
                queue_trb(xhci, ep_ring, false,
                                lower_32_bits(addr),
                                upper_32_bits(addr),
                                length_field,
                                /* We always want to know if the TRB was short,
                                 * or we won't get an event when it completes.
                                 * (Unless we use event data TRBs, which are a
                                 * waste of space and HC resources.)
                                 */
                                field | TRB_ISP | TRB_TYPE(TRB_NORMAL));
                --num_trbs;
                running_total += trb_buff_len;

                /* Calculate length for next transfer --
                 * Are we done queueing all the TRBs for this sg entry?
                 */
                this_sg_len -= trb_buff_len;
                if (this_sg_len == 0) {
                        --num_sgs;
                        if (num_sgs == 0)
                                break;
                        sg = sg_next(sg);
                        addr = (u64) sg_dma_address(sg);
                        this_sg_len = sg_dma_len(sg);
                } else {
                        addr += trb_buff_len;
                }

                trb_buff_len = TRB_MAX_BUFF_SIZE -
                        (addr & ((1 << TRB_MAX_BUFF_SHIFT) - 1));
                trb_buff_len = min_t(int, trb_buff_len, this_sg_len);
                if (running_total + trb_buff_len > urb->transfer_buffer_length)
                        trb_buff_len =
                                urb->transfer_buffer_length - running_total;
        } while (running_total < urb->transfer_buffer_length);

        check_trb_math(urb, num_trbs, running_total);
        giveback_first_trb(xhci, slot_id, ep_index, start_cycle, start_trb, td);
        return 0;
}

/* This is very similar to what ehci-q.c qtd_fill() does */
int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
                struct urb *urb, int slot_id, unsigned int ep_index)
{
        struct xhci_ring *ep_ring;
        struct xhci_td *td;
        int num_trbs;
        struct xhci_generic_trb *start_trb;
        bool first_trb;
        int start_cycle;
        u32 field, length_field;

        int running_total, trb_buff_len, ret;
        u64 addr;

        if (urb->sg)
                return queue_bulk_sg_tx(xhci, mem_flags, urb, slot_id, ep_index);

        ep_ring = xhci->devs[slot_id]->ep_rings[ep_index];

        num_trbs = 0;
        /* How much data is (potentially) left before the 64KB boundary? */
        running_total = TRB_MAX_BUFF_SIZE -
                (urb->transfer_dma & ((1 << TRB_MAX_BUFF_SHIFT) - 1));

        /* If there's some data on this 64KB chunk, or we have to send a
         * zero-length transfer, we need at least one TRB
         */
        if (running_total != 0 || urb->transfer_buffer_length == 0)
                num_trbs++;
        /* How many more 64KB chunks to transfer, how many more TRBs? */
        while (running_total < urb->transfer_buffer_length) {
                num_trbs++;
                running_total += TRB_MAX_BUFF_SIZE;
        }
        /* FIXME: this doesn't deal with URB_ZERO_PACKET - need one more */

        if (!in_interrupt())
                dev_dbg(&urb->dev->dev, "ep %#x - urb len = %#x (%d), addr = %#llx, num_trbs = %d\n",
                                urb->ep->desc.bEndpointAddress,
                                urb->transfer_buffer_length,
                                urb->transfer_buffer_length,
                                (unsigned long long)urb->transfer_dma,
                                num_trbs);

        ret = prepare_transfer(xhci, xhci->devs[slot_id], ep_index,
                        num_trbs, urb, &td, mem_flags);
        if (ret < 0)
                return ret;

        /*
         * Don't give the first TRB to the hardware (by toggling the cycle bit)
         * until we've finished creating all the other TRBs.  The ring's cycle
         * state may change as we enqueue the other TRBs, so save it too.
         */
        start_trb = &ep_ring->enqueue->generic;
        start_cycle = ep_ring->cycle_state;

        running_total = 0;
        /* How much data is in the first TRB? */
        addr = (u64) urb->transfer_dma;
        trb_buff_len = TRB_MAX_BUFF_SIZE -
                (urb->transfer_dma & ((1 << TRB_MAX_BUFF_SHIFT) - 1));
        if (urb->transfer_buffer_length < trb_buff_len)
                trb_buff_len = urb->transfer_buffer_length;

        first_trb = true;

        /* Queue the first TRB, even if it's zero-length */
        do {
                field = 0;

                /* Don't change the cycle bit of the first TRB until later */
                if (first_trb)
                        first_trb = false;
                else
                        field |= ep_ring->cycle_state;

                /* Chain all the TRBs together; clear the chain bit in the last
                 * TRB to indicate it's the last TRB in the chain.
                 */
                if (num_trbs > 1) {
                        field |= TRB_CHAIN;
                } else {
                        /* FIXME - add check for ZERO_PACKET flag before this */
                        td->last_trb = ep_ring->enqueue;
                        field |= TRB_IOC;
                }
                length_field = TRB_LEN(trb_buff_len) |
                        TD_REMAINDER(urb->transfer_buffer_length - running_total) |
                        TRB_INTR_TARGET(0);
                queue_trb(xhci, ep_ring, false,
                                lower_32_bits(addr),
                                upper_32_bits(addr),
                                length_field,
                                /* We always want to know if the TRB was short,
                                 * or we won't get an event when it completes.
                                 * (Unless we use event data TRBs, which are a
                                 * waste of space and HC resources.)
                                 */
                                field | TRB_ISP | TRB_TYPE(TRB_NORMAL));
                --num_trbs;
                running_total += trb_buff_len;

                /* Calculate length for next transfer */
                addr += trb_buff_len;
                trb_buff_len = urb->transfer_buffer_length - running_total;
                if (trb_buff_len > TRB_MAX_BUFF_SIZE)
                        trb_buff_len = TRB_MAX_BUFF_SIZE;
        } while (running_total < urb->transfer_buffer_length);

        check_trb_math(urb, num_trbs, running_total);
        giveback_first_trb(xhci, slot_id, ep_index, start_cycle, start_trb, td);
        return 0;
}

/* Caller must have locked xhci->lock */
int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
                struct urb *urb, int slot_id, unsigned int ep_index)
{
        struct xhci_ring *ep_ring;
        int num_trbs;
        int ret;
        struct usb_ctrlrequest *setup;
        struct xhci_generic_trb *start_trb;
        int start_cycle;
        u32 field, length_field;
        struct xhci_td *td;

        ep_ring = xhci->devs[slot_id]->ep_rings[ep_index];

        /*
         * Need to copy setup packet into setup TRB, so we can't use the setup
         * DMA address.
         */
        if (!urb->setup_packet)
                return -EINVAL;

        if (!in_interrupt())
                xhci_dbg(xhci, "Queueing ctrl tx for slot id %d, ep %d\n",
                                slot_id, ep_index);
        /* 1 TRB for setup, 1 for status */
        num_trbs = 2;
        /*
         * Don't need to check if we need additional event data and normal TRBs,
         * since data in control transfers will never get bigger than 16MB
         * XXX: can we get a buffer that crosses 64KB boundaries?
         */
        if (urb->transfer_buffer_length > 0)
                num_trbs++;
        ret = prepare_transfer(xhci, xhci->devs[slot_id], ep_index, num_trbs,
                        urb, &td, mem_flags);
        if (ret < 0)
                return ret;

        /*
         * Don't give the first TRB to the hardware (by toggling the cycle bit)
         * until we've finished creating all the other TRBs.  The ring's cycle
         * state may change as we enqueue the other TRBs, so save it too.
         */
        start_trb = &ep_ring->enqueue->generic;
        start_cycle = ep_ring->cycle_state;

        /* Queue setup TRB - see section 6.4.1.2.1 */
        /* FIXME better way to translate setup_packet into two u32 fields? */
        setup = (struct usb_ctrlrequest *) urb->setup_packet;
        queue_trb(xhci, ep_ring, false,
                        /* FIXME endianness is probably going to bite my ass here. */
                        setup->bRequestType | setup->bRequest << 8 | setup->wValue << 16,
                        setup->wIndex | setup->wLength << 16,
                        TRB_LEN(8) | TRB_INTR_TARGET(0),
                        /* Immediate data in pointer */
                        TRB_IDT | TRB_TYPE(TRB_SETUP));

        /* If there's data, queue data TRBs */
        field = 0;
        length_field = TRB_LEN(urb->transfer_buffer_length) |
                TD_REMAINDER(urb->transfer_buffer_length) |
                TRB_INTR_TARGET(0);
        if (urb->transfer_buffer_length > 0) {
                if (setup->bRequestType & USB_DIR_IN)
                        field |= TRB_DIR_IN;
                queue_trb(xhci, ep_ring, false,
                                lower_32_bits(urb->transfer_dma),
                                upper_32_bits(urb->transfer_dma),
                                length_field,
                                /* Event on short tx */
                                field | TRB_ISP | TRB_TYPE(TRB_DATA) | ep_ring->cycle_state);
        }

        /* Save the DMA address of the last TRB in the TD */
        td->last_trb = ep_ring->enqueue;

        /* Queue status TRB - see Table 7 and sections 4.11.2.2 and 6.4.1.2.3 */
        /* If the device sent data, the status stage is an OUT transfer */
        if (urb->transfer_buffer_length > 0 && setup->bRequestType & USB_DIR_IN)
                field = 0;
        else
                field = TRB_DIR_IN;
        queue_trb(xhci, ep_ring, false,
                        0,
                        0,
                        TRB_INTR_TARGET(0),
                        /* Event on completion */
                        field | TRB_IOC | TRB_TYPE(TRB_STATUS) | ep_ring->cycle_state);

        giveback_first_trb(xhci, slot_id, ep_index, start_cycle, start_trb, td);
        return 0;
}

/****           Command Ring Operations         ****/

/* Generic function for queueing a command TRB on the command ring */
static int queue_command(struct xhci_hcd *xhci, u32 field1, u32 field2, u32 field3, u32 field4)
{
        if (!room_on_ring(xhci, xhci->cmd_ring, 1)) {
                if (!in_interrupt())
                        xhci_err(xhci, "ERR: No room for command on command ring\n");
                return -ENOMEM;
        }
        queue_trb(xhci, xhci->cmd_ring, false, field1, field2, field3,
                        field4 | xhci->cmd_ring->cycle_state);
        return 0;
}

/* Queue a no-op command on the command ring */
static int queue_cmd_noop(struct xhci_hcd *xhci)
{
        return queue_command(xhci, 0, 0, 0, TRB_TYPE(TRB_CMD_NOOP));
}

/*
 * Place a no-op command on the command ring to test the command and
 * event ring.
 */
void *xhci_setup_one_noop(struct xhci_hcd *xhci)
{
        if (queue_cmd_noop(xhci) < 0)
                return NULL;
        xhci->noops_submitted++;
        return xhci_ring_cmd_db;
}

/* Queue a slot enable or disable request on the command ring */
int xhci_queue_slot_control(struct xhci_hcd *xhci, u32 trb_type, u32 slot_id)
{
        return queue_command(xhci, 0, 0, 0,
                        TRB_TYPE(trb_type) | SLOT_ID_FOR_TRB(slot_id));
}

/* Queue an address device command TRB */
int xhci_queue_address_device(struct xhci_hcd *xhci, dma_addr_t in_ctx_ptr,
                u32 slot_id)
{
        return queue_command(xhci, lower_32_bits(in_ctx_ptr),
                        upper_32_bits(in_ctx_ptr), 0,
                        TRB_TYPE(TRB_ADDR_DEV) | SLOT_ID_FOR_TRB(slot_id));
}

/* Queue a configure endpoint command TRB */
int xhci_queue_configure_endpoint(struct xhci_hcd *xhci, dma_addr_t in_ctx_ptr,
                u32 slot_id)
{
        return queue_command(xhci, lower_32_bits(in_ctx_ptr),
                        upper_32_bits(in_ctx_ptr), 0,
                        TRB_TYPE(TRB_CONFIG_EP) | SLOT_ID_FOR_TRB(slot_id));
}

int xhci_queue_stop_endpoint(struct xhci_hcd *xhci, int slot_id,
                unsigned int ep_index)
{
        u32 trb_slot_id = SLOT_ID_FOR_TRB(slot_id);
        u32 trb_ep_index = EP_ID_FOR_TRB(ep_index);
        u32 type = TRB_TYPE(TRB_STOP_RING);

        return queue_command(xhci, 0, 0, 0,
                        trb_slot_id | trb_ep_index | type);
}

/* Set Transfer Ring Dequeue Pointer command.
 * This should not be used for endpoints that have streams enabled.
 */
static int queue_set_tr_deq(struct xhci_hcd *xhci, int slot_id,
                unsigned int ep_index, struct xhci_segment *deq_seg,
                union xhci_trb *deq_ptr, u32 cycle_state)
{
        dma_addr_t addr;
        u32 trb_slot_id = SLOT_ID_FOR_TRB(slot_id);
        u32 trb_ep_index = EP_ID_FOR_TRB(ep_index);
        u32 type = TRB_TYPE(TRB_SET_DEQ);

        addr = xhci_trb_virt_to_dma(deq_seg, deq_ptr);
        if (addr == 0)
                xhci_warn(xhci, "WARN Cannot submit Set TR Deq Ptr\n");
                xhci_warn(xhci, "WARN deq seg = %p, deq pt = %p\n",
                                deq_seg, deq_ptr);
        return queue_command(xhci, lower_32_bits(addr) | cycle_state,
                        upper_32_bits(addr), 0,
                        trb_slot_id | trb_ep_index | type);
}

int xhci_queue_reset_ep(struct xhci_hcd *xhci, int slot_id,
                unsigned int ep_index)
{
        u32 trb_slot_id = SLOT_ID_FOR_TRB(slot_id);
        u32 trb_ep_index = EP_ID_FOR_TRB(ep_index);
        u32 type = TRB_TYPE(TRB_RESET_EP);

        return queue_command(xhci, 0, 0, 0, trb_slot_id | trb_ep_index | type);
}