[deliverable/linux.git] / drivers / char / drm / via_dmablit.c

/* via_dmablit.c -- PCI DMA BitBlt support for the VIA Unichrome/Pro
 * 
 * Copyright (C) 2005 Thomas Hellstrom, All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sub license,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, 
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR 
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE 
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * Authors: 
 *    Thomas Hellstrom.
 *    Partially based on code obtained from Digeo Inc.
 */


/*
 * Unmaps the DMA mappings. 
 * FIXME: Is this a NoOp on x86? Also 
 * FIXME: What happens if this one is called and a pending blit has previously done 
 * the same DMA mappings? 
 */

#include "drmP.h"
#include "via_drm.h"
#include "via_drv.h"
#include "via_dmablit.h"

#include <linux/pagemap.h>

#define VIA_PGDN(x)          (((unsigned long)(x)) & PAGE_MASK)
#define VIA_PGOFF(x)        (((unsigned long)(x)) & ~PAGE_MASK)
#define VIA_PFN(x)            ((unsigned long)(x) >> PAGE_SHIFT)

typedef struct _drm_via_descriptor {
        uint32_t mem_addr;
        uint32_t dev_addr;
        uint32_t size;
        uint32_t next;
} drm_via_descriptor_t;


/*
 * Unmap a DMA mapping.
 */



static void
via_unmap_blit_from_device(struct pci_dev *pdev, drm_via_sg_info_t *vsg)
{
        int num_desc = vsg->num_desc;
        unsigned cur_descriptor_page = num_desc / vsg->descriptors_per_page;
        unsigned descriptor_this_page = num_desc % vsg->descriptors_per_page;
        drm_via_descriptor_t *desc_ptr = vsg->desc_pages[cur_descriptor_page] + 
                descriptor_this_page;
        dma_addr_t next = vsg->chain_start;

        while(num_desc--) {
                if (descriptor_this_page-- == 0) {
                        cur_descriptor_page--;
                        descriptor_this_page = vsg->descriptors_per_page - 1;
                        desc_ptr = vsg->desc_pages[cur_descriptor_page] + 
                                descriptor_this_page;
                }
                dma_unmap_single(&pdev->dev, next, sizeof(*desc_ptr), DMA_TO_DEVICE);
                dma_unmap_page(&pdev->dev, desc_ptr->mem_addr, desc_ptr->size, vsg->direction);
                next = (dma_addr_t) desc_ptr->next;
                desc_ptr--;
        }
}

/*
 * If mode = 0, count how many descriptors are needed.
 * If mode = 1, Map the DMA pages for the device, put together and map also the descriptors.
 * Descriptors are run in reverse order by the hardware because we are not allowed to update the
 * 'next' field without syncing calls when the descriptor is already mapped.
 */

static void
via_map_blit_for_device(struct pci_dev *pdev,
                   const drm_via_dmablit_t *xfer,
                   drm_via_sg_info_t *vsg, 
                   int mode)
{
        unsigned cur_descriptor_page = 0;
        unsigned num_descriptors_this_page = 0;
        unsigned char *mem_addr = xfer->mem_addr;
        unsigned char *cur_mem;
        unsigned char *first_addr = (unsigned char *)VIA_PGDN(mem_addr);
        uint32_t fb_addr = xfer->fb_addr;
        uint32_t cur_fb;
        unsigned long line_len;
        unsigned remaining_len;
        int num_desc = 0;
        int cur_line;
        dma_addr_t next = 0 | VIA_DMA_DPR_EC;
        drm_via_descriptor_t *desc_ptr = NULL;

        if (mode == 1) 
                desc_ptr = vsg->desc_pages[cur_descriptor_page];

        for (cur_line = 0; cur_line < xfer->num_lines; ++cur_line) {

                line_len = xfer->line_length;
                cur_fb = fb_addr;
                cur_mem = mem_addr;
                
                while (line_len > 0) {

                        remaining_len = min(PAGE_SIZE-VIA_PGOFF(cur_mem), line_len);
                        line_len -= remaining_len;

                        if (mode == 1) {
                                desc_ptr->mem_addr = 
                                        dma_map_page(&pdev->dev, 
                                                     vsg->pages[VIA_PFN(cur_mem) - 
                                                                VIA_PFN(first_addr)],
                                                     VIA_PGOFF(cur_mem), remaining_len, 
                                                     vsg->direction);
                                desc_ptr->dev_addr = cur_fb;
                                
                                desc_ptr->size = remaining_len;
                                desc_ptr->next = (uint32_t) next;
                                next = dma_map_single(&pdev->dev, desc_ptr, sizeof(*desc_ptr), 
                                                      DMA_TO_DEVICE);
                                desc_ptr++;
                                if (++num_descriptors_this_page >= vsg->descriptors_per_page) {
                                        num_descriptors_this_page = 0;
                                        desc_ptr = vsg->desc_pages[++cur_descriptor_page];
                                }
                        }
                        
                        num_desc++;
                        cur_mem += remaining_len;
                        cur_fb += remaining_len;
                }
                
                mem_addr += xfer->mem_stride;
                fb_addr += xfer->fb_stride;
        }

        if (mode == 1) {
                vsg->chain_start = next;
                vsg->state = dr_via_device_mapped;
        }
        vsg->num_desc = num_desc;
}

/*
 * Function that frees up all resources for a blit. It is usable even if the 
 * blit info has only been partially built as long as the status enum is consistent
 * with the actual status of the used resources.
 */


static void
via_free_sg_info(struct pci_dev *pdev, drm_via_sg_info_t *vsg) 
{
        struct page *page;
        int i;

        switch(vsg->state) {
        case dr_via_device_mapped:
                via_unmap_blit_from_device(pdev, vsg);
        case dr_via_desc_pages_alloc:
                for (i=0; i<vsg->num_desc_pages; ++i) {
                        if (vsg->desc_pages[i] != NULL)
                          free_page((unsigned long)vsg->desc_pages[i]);
                }
                kfree(vsg->desc_pages);
        case dr_via_pages_locked:
                for (i=0; i<vsg->num_pages; ++i) {
                        if ( NULL != (page = vsg->pages[i])) {
                                if (! PageReserved(page) && (DMA_FROM_DEVICE == vsg->direction)) 
                                        SetPageDirty(page);
                                page_cache_release(page);
                        }
                }
        case dr_via_pages_alloc:
                vfree(vsg->pages);
        default:
                vsg->state = dr_via_sg_init;
        }
        if (vsg->bounce_buffer) {
                vfree(vsg->bounce_buffer);
                vsg->bounce_buffer = NULL;
        }
        vsg->free_on_sequence = 0;
}               

/*
 * Fire a blit engine.
 */

static void
via_fire_dmablit(drm_device_t *dev, drm_via_sg_info_t *vsg, int engine)
{
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;

        VIA_WRITE(VIA_PCI_DMA_MAR0 + engine*0x10, 0);
        VIA_WRITE(VIA_PCI_DMA_DAR0 + engine*0x10, 0);
        VIA_WRITE(VIA_PCI_DMA_CSR0 + engine*0x04, VIA_DMA_CSR_DD | VIA_DMA_CSR_TD | 
                  VIA_DMA_CSR_DE);
        VIA_WRITE(VIA_PCI_DMA_MR0  + engine*0x04, VIA_DMA_MR_CM | VIA_DMA_MR_TDIE);
        VIA_WRITE(VIA_PCI_DMA_BCR0 + engine*0x10, 0);
        VIA_WRITE(VIA_PCI_DMA_DPR0 + engine*0x10, vsg->chain_start);
        DRM_WRITEMEMORYBARRIER();
        VIA_WRITE(VIA_PCI_DMA_CSR0 + engine*0x04, VIA_DMA_CSR_DE | VIA_DMA_CSR_TS);
        VIA_READ(VIA_PCI_DMA_CSR0 + engine*0x04);
}

/*
 * Obtain a page pointer array and lock all pages into system memory. A segmentation violation will
 * occur here if the calling user does not have access to the submitted address.
 */

static int
via_lock_all_dma_pages(drm_via_sg_info_t *vsg,  drm_via_dmablit_t *xfer)
{
        int ret;
        unsigned long first_pfn = VIA_PFN(xfer->mem_addr);
        vsg->num_pages = VIA_PFN(xfer->mem_addr + (xfer->num_lines * xfer->mem_stride -1)) - 
                first_pfn + 1;
        
        if (NULL == (vsg->pages = vmalloc(sizeof(struct page *) * vsg->num_pages)))
                return DRM_ERR(ENOMEM);
        memset(vsg->pages, 0, sizeof(struct page *) * vsg->num_pages);
        down_read(&current->mm->mmap_sem);
        ret = get_user_pages(current, current->mm,
                             (unsigned long)xfer->mem_addr,
                             vsg->num_pages,
                             (vsg->direction == DMA_FROM_DEVICE),
                             0, vsg->pages, NULL);

        up_read(&current->mm->mmap_sem);
        if (ret != vsg->num_pages) {
                if (ret < 0) 
                        return ret;
                vsg->state = dr_via_pages_locked;
                return DRM_ERR(EINVAL);
        }
        vsg->state = dr_via_pages_locked;
        DRM_DEBUG("DMA pages locked\n");
        return 0;
}

/*
 * Allocate DMA capable memory for the blit descriptor chain, and an array that keeps track of the
 * pages we allocate. We don't want to use kmalloc for the descriptor chain because it may be
 * quite large for some blits, and pages don't need to be contingous.
 */

static int 
via_alloc_desc_pages(drm_via_sg_info_t *vsg)
{
        int i;
        
        vsg->descriptors_per_page = PAGE_SIZE / sizeof( drm_via_descriptor_t);
        vsg->num_desc_pages = (vsg->num_desc + vsg->descriptors_per_page - 1) / 
                vsg->descriptors_per_page;

        if (NULL ==  (vsg->desc_pages = kmalloc(sizeof(void *) * vsg->num_desc_pages, GFP_KERNEL))) 
                return DRM_ERR(ENOMEM);
        
        memset(vsg->desc_pages, 0, sizeof(void *) * vsg->num_desc_pages);
        vsg->state = dr_via_desc_pages_alloc;
        for (i=0; i<vsg->num_desc_pages; ++i) {
                if (NULL == (vsg->desc_pages[i] = 
                             (drm_via_descriptor_t *) __get_free_page(GFP_KERNEL)))
                        return DRM_ERR(ENOMEM);
        }
        DRM_DEBUG("Allocated %d pages for %d descriptors.\n", vsg->num_desc_pages,
                  vsg->num_desc);
        return 0;
}
                        
static void
via_abort_dmablit(drm_device_t *dev, int engine)
{
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;

        VIA_WRITE(VIA_PCI_DMA_CSR0 + engine*0x04, VIA_DMA_CSR_TA);
}

static void
via_dmablit_engine_off(drm_device_t *dev, int engine)
{
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;

        VIA_WRITE(VIA_PCI_DMA_CSR0 + engine*0x04, VIA_DMA_CSR_TD | VIA_DMA_CSR_DD); 
}



/*
 * The dmablit part of the IRQ handler. Trying to do only reasonably fast things here.
 * The rest, like unmapping and freeing memory for done blits is done in a separate workqueue
 * task. Basically the task of the interrupt handler is to submit a new blit to the engine, while
 * the workqueue task takes care of processing associated with the old blit.
 */
                
void
via_dmablit_handler(drm_device_t *dev, int engine, int from_irq)
{
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;
        drm_via_blitq_t *blitq = dev_priv->blit_queues + engine;
        int cur;
        int done_transfer;
        unsigned long irqsave=0;
        uint32_t status = 0;

        DRM_DEBUG("DMA blit handler called. engine = %d, from_irq = %d, blitq = 0x%lx\n",
                  engine, from_irq, (unsigned long) blitq);

        if (from_irq) {
                spin_lock(&blitq->blit_lock);
        } else {
                spin_lock_irqsave(&blitq->blit_lock, irqsave);
        }

        done_transfer = blitq->is_active && 
          (( status = VIA_READ(VIA_PCI_DMA_CSR0 + engine*0x04)) & VIA_DMA_CSR_TD);
        done_transfer = done_transfer || ( blitq->aborting && !(status & VIA_DMA_CSR_DE)); 

        cur = blitq->cur;
        if (done_transfer) {

                blitq->blits[cur]->aborted = blitq->aborting;
                blitq->done_blit_handle++;
                DRM_WAKEUP(blitq->blit_queue + cur);            

                cur++;
                if (cur >= VIA_NUM_BLIT_SLOTS) 
                        cur = 0;
                blitq->cur = cur;

                /*
                 * Clear transfer done flag.
                 */

                VIA_WRITE(VIA_PCI_DMA_CSR0 + engine*0x04,  VIA_DMA_CSR_TD);

                blitq->is_active = 0;
                blitq->aborting = 0;
                schedule_work(&blitq->wq);      

        } else if (blitq->is_active && time_after_eq(jiffies, blitq->end)) {

                /*
                 * Abort transfer after one second.
                 */

                via_abort_dmablit(dev, engine);
                blitq->aborting = 1;
                blitq->end = jiffies + DRM_HZ;
        }
                        
        if (!blitq->is_active) {
                if (blitq->num_outstanding) {
                        via_fire_dmablit(dev, blitq->blits[cur], engine);
                        blitq->is_active = 1;
                        blitq->cur = cur;
                        blitq->num_outstanding--;
                        blitq->end = jiffies + DRM_HZ;
                        if (!timer_pending(&blitq->poll_timer))
                                mod_timer(&blitq->poll_timer, jiffies + 1);
                } else {
                        if (timer_pending(&blitq->poll_timer)) {
                                del_timer(&blitq->poll_timer);
                        }
                        via_dmablit_engine_off(dev, engine);
                }
        }               

        if (from_irq) {
                spin_unlock(&blitq->blit_lock);
        } else {
                spin_unlock_irqrestore(&blitq->blit_lock, irqsave);
        }
} 



/*
 * Check whether this blit is still active, performing necessary locking.
 */

static int
via_dmablit_active(drm_via_blitq_t *blitq, int engine, uint32_t handle, wait_queue_head_t **queue)
{
        unsigned long irqsave;
        uint32_t slot;
        int active;

        spin_lock_irqsave(&blitq->blit_lock, irqsave);

        /*
         * Allow for handle wraparounds.
         */

        active = ((blitq->done_blit_handle - handle) > (1 << 23)) &&
                ((blitq->cur_blit_handle - handle) <= (1 << 23));

        if (queue && active) {
                slot = handle - blitq->done_blit_handle + blitq->cur -1;
                if (slot >= VIA_NUM_BLIT_SLOTS) {
                        slot -= VIA_NUM_BLIT_SLOTS;
                }
                *queue = blitq->blit_queue + slot;
        }

        spin_unlock_irqrestore(&blitq->blit_lock, irqsave);

        return active;
}
        
/*
 * Sync. Wait for at least three seconds for the blit to be performed.
 */

static int
via_dmablit_sync(drm_device_t *dev, uint32_t handle, int engine) 
{

        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;
        drm_via_blitq_t *blitq = dev_priv->blit_queues + engine;
        wait_queue_head_t *queue;
        int ret = 0;

        if (via_dmablit_active(blitq, engine, handle, &queue)) {
                DRM_WAIT_ON(ret, *queue, 3 * DRM_HZ, 
                            !via_dmablit_active(blitq, engine, handle, NULL));
        }
        DRM_DEBUG("DMA blit sync handle 0x%x engine %d returned %d\n",
                  handle, engine, ret);
        
        return ret;
}


/*
 * A timer that regularly polls the blit engine in cases where we don't have interrupts:
 * a) Broken hardware (typically those that don't have any video capture facility).
 * b) Blit abort. The hardware doesn't send an interrupt when a blit is aborted.
 * The timer and hardware IRQ's can and do work in parallel. If the hardware has
 * irqs, it will shorten the latency somewhat.
 */



static void
via_dmablit_timer(unsigned long data)
{
        drm_via_blitq_t *blitq = (drm_via_blitq_t *) data;
        drm_device_t *dev = blitq->dev;
        int engine = (int)
                (blitq - ((drm_via_private_t *)dev->dev_private)->blit_queues);
                
        DRM_DEBUG("Polling timer called for engine %d, jiffies %lu\n", engine, 
                  (unsigned long) jiffies);

        via_dmablit_handler(dev, engine, 0);
        
        if (!timer_pending(&blitq->poll_timer)) {
                mod_timer(&blitq->poll_timer, jiffies + 1);

               /*
                * Rerun handler to delete timer if engines are off, and
                * to shorten abort latency. This is a little nasty.
                */

               via_dmablit_handler(dev, engine, 0);

        }
}




/*
 * Workqueue task that frees data and mappings associated with a blit.
 * Also wakes up waiting processes. Each of these tasks handles one
 * blit engine only and may not be called on each interrupt.
 */


static void 
via_dmablit_workqueue(struct work_struct *work)
{
        drm_via_blitq_t *blitq = container_of(work, drm_via_blitq_t, wq);
        drm_device_t *dev = blitq->dev;
        unsigned long irqsave;
        drm_via_sg_info_t *cur_sg;
        int cur_released;
        
        
        DRM_DEBUG("Workqueue task called for blit engine %ld\n",(unsigned long) 
                  (blitq - ((drm_via_private_t *)dev->dev_private)->blit_queues));

        spin_lock_irqsave(&blitq->blit_lock, irqsave);
        
        while(blitq->serviced != blitq->cur) {

                cur_released = blitq->serviced++;

                DRM_DEBUG("Releasing blit slot %d\n", cur_released);

                if (blitq->serviced >= VIA_NUM_BLIT_SLOTS) 
                        blitq->serviced = 0;
                
                cur_sg = blitq->blits[cur_released];
                blitq->num_free++;
                                
                spin_unlock_irqrestore(&blitq->blit_lock, irqsave);
                
                DRM_WAKEUP(&blitq->busy_queue);
                
                via_free_sg_info(dev->pdev, cur_sg);
                kfree(cur_sg);
                
                spin_lock_irqsave(&blitq->blit_lock, irqsave);
        }

        spin_unlock_irqrestore(&blitq->blit_lock, irqsave);
}
        

/*
 * Init all blit engines. Currently we use two, but some hardware have 4.
 */


void
via_init_dmablit(drm_device_t *dev)
{
        int i,j;
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;
        drm_via_blitq_t *blitq;

        pci_set_master(dev->pdev);      
        
        for (i=0; i< VIA_NUM_BLIT_ENGINES; ++i) {
                blitq = dev_priv->blit_queues + i;
                blitq->dev = dev;
                blitq->cur_blit_handle = 0;
                blitq->done_blit_handle = 0;
                blitq->head = 0;
                blitq->cur = 0;
                blitq->serviced = 0;
                blitq->num_free = VIA_NUM_BLIT_SLOTS;
                blitq->num_outstanding = 0;
                blitq->is_active = 0;
                blitq->aborting = 0;
                spin_lock_init(&blitq->blit_lock);
                for (j=0; j<VIA_NUM_BLIT_SLOTS; ++j) {
                        DRM_INIT_WAITQUEUE(blitq->blit_queue + j);
                }
                DRM_INIT_WAITQUEUE(&blitq->busy_queue);
                INIT_WORK(&blitq->wq, via_dmablit_workqueue);
                setup_timer(&blitq->poll_timer, via_dmablit_timer,
                                (unsigned long)blitq);
        }       
}

/*
 * Build all info and do all mappings required for a blit.
 */
                

static int
via_build_sg_info(drm_device_t *dev, drm_via_sg_info_t *vsg, drm_via_dmablit_t *xfer)
{
        int draw = xfer->to_fb;
        int ret = 0;
        
        vsg->direction = (draw) ? DMA_TO_DEVICE : DMA_FROM_DEVICE;
        vsg->bounce_buffer = NULL;

        vsg->state = dr_via_sg_init;

        if (xfer->num_lines <= 0 || xfer->line_length <= 0) {
                DRM_ERROR("Zero size bitblt.\n");
                return DRM_ERR(EINVAL);
        }

        /*
         * Below check is a driver limitation, not a hardware one. We
         * don't want to lock unused pages, and don't want to incoporate the
         * extra logic of avoiding them. Make sure there are no. 
         * (Not a big limitation anyway.)
         */

        if ((xfer->mem_stride - xfer->line_length) >= PAGE_SIZE) {
                DRM_ERROR("Too large system memory stride. Stride: %d, "
                          "Length: %d\n", xfer->mem_stride, xfer->line_length);
                return DRM_ERR(EINVAL);
        }

        if ((xfer->mem_stride == xfer->line_length) &&
           (xfer->fb_stride == xfer->line_length)) {
                xfer->mem_stride *= xfer->num_lines;
                xfer->line_length = xfer->mem_stride;
                xfer->fb_stride = xfer->mem_stride;
                xfer->num_lines = 1;
        }

        /*
         * Don't lock an arbitrary large number of pages, since that causes a
         * DOS security hole.
         */

        if (xfer->num_lines > 2048 || (xfer->num_lines*xfer->mem_stride > (2048*2048*4))) {
                DRM_ERROR("Too large PCI DMA bitblt.\n");
                return DRM_ERR(EINVAL);
        }               

        /* 
         * we allow a negative fb stride to allow flipping of images in
         * transfer. 
         */

        if (xfer->mem_stride < xfer->line_length ||
                abs(xfer->fb_stride) < xfer->line_length) {
                DRM_ERROR("Invalid frame-buffer / memory stride.\n");
                return DRM_ERR(EINVAL);
        }

        /*
         * A hardware bug seems to be worked around if system memory addresses start on
         * 16 byte boundaries. This seems a bit restrictive however. VIA is contacted
         * about this. Meanwhile, impose the following restrictions:
         */

#ifdef VIA_BUGFREE
        if ((((unsigned long)xfer->mem_addr & 3) != ((unsigned long)xfer->fb_addr & 3)) ||
            ((xfer->num_lines > 1) && ((xfer->mem_stride & 3) != (xfer->fb_stride & 3)))) {
                DRM_ERROR("Invalid DRM bitblt alignment.\n");
                return DRM_ERR(EINVAL);
        }
#else
        if ((((unsigned long)xfer->mem_addr & 15) ||
              ((unsigned long)xfer->fb_addr & 3)) ||
           ((xfer->num_lines > 1) && 
           ((xfer->mem_stride & 15) || (xfer->fb_stride & 3)))) {
                DRM_ERROR("Invalid DRM bitblt alignment.\n");
                return DRM_ERR(EINVAL);
        }       
#endif

        if (0 != (ret = via_lock_all_dma_pages(vsg, xfer))) {
                DRM_ERROR("Could not lock DMA pages.\n");
                via_free_sg_info(dev->pdev, vsg);
                return ret;
        }

        via_map_blit_for_device(dev->pdev, xfer, vsg, 0);
        if (0 != (ret = via_alloc_desc_pages(vsg))) {
                DRM_ERROR("Could not allocate DMA descriptor pages.\n");
                via_free_sg_info(dev->pdev, vsg);
                return ret;
        }
        via_map_blit_for_device(dev->pdev, xfer, vsg, 1);
        
        return 0;
}
        

/*
 * Reserve one free slot in the blit queue. Will wait for one second for one
 * to become available. Otherwise -EBUSY is returned.
 */

static int 
via_dmablit_grab_slot(drm_via_blitq_t *blitq, int engine)
{
        int ret=0;
        unsigned long irqsave;

        DRM_DEBUG("Num free is %d\n", blitq->num_free);
        spin_lock_irqsave(&blitq->blit_lock, irqsave);
        while(blitq->num_free == 0) {
                spin_unlock_irqrestore(&blitq->blit_lock, irqsave);

                DRM_WAIT_ON(ret, blitq->busy_queue, DRM_HZ, blitq->num_free > 0);
                if (ret) {
                        return (DRM_ERR(EINTR) == ret) ? DRM_ERR(EAGAIN) : ret;
                }
                
                spin_lock_irqsave(&blitq->blit_lock, irqsave);
        }
        
        blitq->num_free--;
        spin_unlock_irqrestore(&blitq->blit_lock, irqsave);

        return 0;
}

/*
 * Hand back a free slot if we changed our mind.
 */

static void 
via_dmablit_release_slot(drm_via_blitq_t *blitq)
{
        unsigned long irqsave;

        spin_lock_irqsave(&blitq->blit_lock, irqsave);
        blitq->num_free++;
        spin_unlock_irqrestore(&blitq->blit_lock, irqsave);
        DRM_WAKEUP( &blitq->busy_queue );
}

/*
 * Grab a free slot. Build blit info and queue a blit.
 */


static int 
via_dmablit(drm_device_t *dev, drm_via_dmablit_t *xfer)  
{
        drm_via_private_t *dev_priv = (drm_via_private_t *)dev->dev_private;
        drm_via_sg_info_t *vsg;
        drm_via_blitq_t *blitq;
        int ret;
        int engine;
        unsigned long irqsave;

        if (dev_priv == NULL) {
                DRM_ERROR("Called without initialization.\n");
                return DRM_ERR(EINVAL);
        }

        engine = (xfer->to_fb) ? 0 : 1;
        blitq = dev_priv->blit_queues + engine;
        if (0 != (ret = via_dmablit_grab_slot(blitq, engine))) {
                return ret;
        }
        if (NULL == (vsg = kmalloc(sizeof(*vsg), GFP_KERNEL))) {
                via_dmablit_release_slot(blitq);
                return DRM_ERR(ENOMEM);
        }
        if (0 != (ret = via_build_sg_info(dev, vsg, xfer))) {
                via_dmablit_release_slot(blitq);
                kfree(vsg);
                return ret;
        }
        spin_lock_irqsave(&blitq->blit_lock, irqsave);

        blitq->blits[blitq->head++] = vsg;
        if (blitq->head >= VIA_NUM_BLIT_SLOTS) 
                blitq->head = 0;
        blitq->num_outstanding++;
        xfer->sync.sync_handle = ++blitq->cur_blit_handle; 

        spin_unlock_irqrestore(&blitq->blit_lock, irqsave);
        xfer->sync.engine = engine;

        via_dmablit_handler(dev, engine, 0);

        return 0;
}

/*
 * Sync on a previously submitted blit. Note that the X server use signals extensively, and
 * that there is a very big probability that this IOCTL will be interrupted by a signal. In that
 * case it returns with -EAGAIN for the signal to be delivered. 
 * The caller should then reissue the IOCTL. This is similar to what is being done for drmGetLock().
 */

int
via_dma_blit_sync( DRM_IOCTL_ARGS )
{
        drm_via_blitsync_t sync;
        int err;
        DRM_DEVICE;

        DRM_COPY_FROM_USER_IOCTL(sync, (drm_via_blitsync_t *)data, sizeof(sync));
        
        if (sync.engine >= VIA_NUM_BLIT_ENGINES) 
                return DRM_ERR(EINVAL);

        err = via_dmablit_sync(dev, sync.sync_handle, sync.engine);

        if (DRM_ERR(EINTR) == err)
                err = DRM_ERR(EAGAIN);

        return err;
}
        

/*
 * Queue a blit and hand back a handle to be used for sync. This IOCTL may be interrupted by a signal
 * while waiting for a free slot in the blit queue. In that case it returns with -EAGAIN and should 
 * be reissued. See the above IOCTL code.
 */

int 
via_dma_blit( DRM_IOCTL_ARGS )
{
        drm_via_dmablit_t xfer;
        int err;
        DRM_DEVICE;

        DRM_COPY_FROM_USER_IOCTL(xfer, (drm_via_dmablit_t __user *)data, sizeof(xfer));

        err = via_dmablit(dev, &xfer);

        DRM_COPY_TO_USER_IOCTL((void __user *)data, xfer, sizeof(xfer));

        return err;
}