mac80211: push rx status into skb->cb

[deliverable/linux.git] / drivers / net / wireless / ath / ath9k / recv.c

/*
 * Copyright (c) 2008-2009 Atheros Communications Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include "ath9k.h"

static struct ieee80211_hw * ath_get_virt_hw(struct ath_softc *sc,
                                             struct ieee80211_hdr *hdr)
{
        struct ieee80211_hw *hw = sc->pri_wiphy->hw;
        int i;

        spin_lock_bh(&sc->wiphy_lock);
        for (i = 0; i < sc->num_sec_wiphy; i++) {
                struct ath_wiphy *aphy = sc->sec_wiphy[i];
                if (aphy == NULL)
                        continue;
                if (compare_ether_addr(hdr->addr1, aphy->hw->wiphy->perm_addr)
                    == 0) {
                        hw = aphy->hw;
                        break;
                }
        }
        spin_unlock_bh(&sc->wiphy_lock);
        return hw;
}

/*
 * Setup and link descriptors.
 *
 * 11N: we can no longer afford to self link the last descriptor.
 * MAC acknowledges BA status as long as it copies frames to host
 * buffer (or rx fifo). This can incorrectly acknowledge packets
 * to a sender if last desc is self-linked.
 */
static void ath_rx_buf_link(struct ath_softc *sc, struct ath_buf *bf)
{
        struct ath_hw *ah = sc->sc_ah;
        struct ath_desc *ds;
        struct sk_buff *skb;

        ATH_RXBUF_RESET(bf);

        ds = bf->bf_desc;
        ds->ds_link = 0; /* link to null */
        ds->ds_data = bf->bf_buf_addr;

        /* virtual addr of the beginning of the buffer. */
        skb = bf->bf_mpdu;
        ASSERT(skb != NULL);
        ds->ds_vdata = skb->data;

        /* setup rx descriptors. The rx.bufsize here tells the harware
         * how much data it can DMA to us and that we are prepared
         * to process */
        ath9k_hw_setuprxdesc(ah, ds,
                             sc->rx.bufsize,
                             0);

        if (sc->rx.rxlink == NULL)
                ath9k_hw_putrxbuf(ah, bf->bf_daddr);
        else
                *sc->rx.rxlink = bf->bf_daddr;

        sc->rx.rxlink = &ds->ds_link;
        ath9k_hw_rxena(ah);
}

static void ath_setdefantenna(struct ath_softc *sc, u32 antenna)
{
        /* XXX block beacon interrupts */
        ath9k_hw_setantenna(sc->sc_ah, antenna);
        sc->rx.defant = antenna;
        sc->rx.rxotherant = 0;
}

/*
 *  Extend 15-bit time stamp from rx descriptor to
 *  a full 64-bit TSF using the current h/w TSF.
*/
static u64 ath_extend_tsf(struct ath_softc *sc, u32 rstamp)
{
        u64 tsf;

        tsf = ath9k_hw_gettsf64(sc->sc_ah);
        if ((tsf & 0x7fff) < rstamp)
                tsf -= 0x8000;
        return (tsf & ~0x7fff) | rstamp;
}

static struct sk_buff *ath_rxbuf_alloc(struct ath_softc *sc, u32 len, gfp_t gfp_mask)
{
        struct sk_buff *skb;
        u32 off;

        /*
         * Cache-line-align.  This is important (for the
         * 5210 at least) as not doing so causes bogus data
         * in rx'd frames.
         */

        /* Note: the kernel can allocate a value greater than
         * what we ask it to give us. We really only need 4 KB as that
         * is this hardware supports and in fact we need at least 3849
         * as that is the MAX AMSDU size this hardware supports.
         * Unfortunately this means we may get 8 KB here from the
         * kernel... and that is actually what is observed on some
         * systems :( */
        skb = __dev_alloc_skb(len + sc->cachelsz - 1, gfp_mask);
        if (skb != NULL) {
                off = ((unsigned long) skb->data) % sc->cachelsz;
                if (off != 0)
                        skb_reserve(skb, sc->cachelsz - off);
        } else {
                DPRINTF(sc, ATH_DBG_FATAL,
                        "skbuff alloc of size %u failed\n", len);
                return NULL;
        }

        return skb;
}

/*
 * For Decrypt or Demic errors, we only mark packet status here and always push
 * up the frame up to let mac80211 handle the actual error case, be it no
 * decryption key or real decryption error. This let us keep statistics there.
 */
static int ath_rx_prepare(struct sk_buff *skb, struct ath_desc *ds,
                          struct ieee80211_rx_status *rx_status, bool *decrypt_error,
                          struct ath_softc *sc)
{
        struct ieee80211_hdr *hdr;
        u8 ratecode;
        __le16 fc;
        struct ieee80211_hw *hw;

        hdr = (struct ieee80211_hdr *)skb->data;
        fc = hdr->frame_control;
        memset(rx_status, 0, sizeof(struct ieee80211_rx_status));
        hw = ath_get_virt_hw(sc, hdr);

        if (ds->ds_rxstat.rs_more) {
                /*
                 * Frame spans multiple descriptors; this cannot happen yet
                 * as we don't support jumbograms. If not in monitor mode,
                 * discard the frame. Enable this if you want to see
                 * error frames in Monitor mode.
                 */
                if (sc->sc_ah->opmode != NL80211_IFTYPE_MONITOR)
                        goto rx_next;
        } else if (ds->ds_rxstat.rs_status != 0) {
                if (ds->ds_rxstat.rs_status & ATH9K_RXERR_CRC)
                        rx_status->flag |= RX_FLAG_FAILED_FCS_CRC;
                if (ds->ds_rxstat.rs_status & ATH9K_RXERR_PHY)
                        goto rx_next;

                if (ds->ds_rxstat.rs_status & ATH9K_RXERR_DECRYPT) {
                        *decrypt_error = true;
                } else if (ds->ds_rxstat.rs_status & ATH9K_RXERR_MIC) {
                        if (ieee80211_is_ctl(fc))
                                /*
                                 * Sometimes, we get invalid
                                 * MIC failures on valid control frames.
                                 * Remove these mic errors.
                                 */
                                ds->ds_rxstat.rs_status &= ~ATH9K_RXERR_MIC;
                        else
                                rx_status->flag |= RX_FLAG_MMIC_ERROR;
                }
                /*
                 * Reject error frames with the exception of
                 * decryption and MIC failures. For monitor mode,
                 * we also ignore the CRC error.
                 */
                if (sc->sc_ah->opmode == NL80211_IFTYPE_MONITOR) {
                        if (ds->ds_rxstat.rs_status &
                            ~(ATH9K_RXERR_DECRYPT | ATH9K_RXERR_MIC |
                              ATH9K_RXERR_CRC))
                                goto rx_next;
                } else {
                        if (ds->ds_rxstat.rs_status &
                            ~(ATH9K_RXERR_DECRYPT | ATH9K_RXERR_MIC)) {
                                goto rx_next;
                        }
                }
        }

        ratecode = ds->ds_rxstat.rs_rate;

        if (ratecode & 0x80) {
                /* HT rate */
                rx_status->flag |= RX_FLAG_HT;
                if (ds->ds_rxstat.rs_flags & ATH9K_RX_2040)
                        rx_status->flag |= RX_FLAG_40MHZ;
                if (ds->ds_rxstat.rs_flags & ATH9K_RX_GI)
                        rx_status->flag |= RX_FLAG_SHORT_GI;
                rx_status->rate_idx = ratecode & 0x7f;
        } else {
                int i = 0, cur_band, n_rates;

                cur_band = hw->conf.channel->band;
                n_rates = sc->sbands[cur_band].n_bitrates;

                for (i = 0; i < n_rates; i++) {
                        if (sc->sbands[cur_band].bitrates[i].hw_value ==
                            ratecode) {
                                rx_status->rate_idx = i;
                                break;
                        }

                        if (sc->sbands[cur_band].bitrates[i].hw_value_short ==
                            ratecode) {
                                rx_status->rate_idx = i;
                                rx_status->flag |= RX_FLAG_SHORTPRE;
                                break;
                        }
                }
        }

        rx_status->mactime = ath_extend_tsf(sc, ds->ds_rxstat.rs_tstamp);
        rx_status->band = hw->conf.channel->band;
        rx_status->freq = hw->conf.channel->center_freq;
        rx_status->noise = sc->ani.noise_floor;
        rx_status->signal = rx_status->noise + ds->ds_rxstat.rs_rssi;
        rx_status->antenna = ds->ds_rxstat.rs_antenna;

        /* at 45 you will be able to use MCS 15 reliably. A more elaborate
         * scheme can be used here but it requires tables of SNR/throughput for
         * each possible mode used. */
        rx_status->qual =  ds->ds_rxstat.rs_rssi * 100 / 45;

        /* rssi can be more than 45 though, anything above that
         * should be considered at 100% */
        if (rx_status->qual > 100)
                rx_status->qual = 100;

        rx_status->flag |= RX_FLAG_TSFT;

        return 1;
rx_next:
        return 0;
}

static void ath_opmode_init(struct ath_softc *sc)
{
        struct ath_hw *ah = sc->sc_ah;
        u32 rfilt, mfilt[2];

        /* configure rx filter */
        rfilt = ath_calcrxfilter(sc);
        ath9k_hw_setrxfilter(ah, rfilt);

        /* configure bssid mask */
        if (ah->caps.hw_caps & ATH9K_HW_CAP_BSSIDMASK)
                ath9k_hw_setbssidmask(sc);

        /* configure operational mode */
        ath9k_hw_setopmode(ah);

        /* Handle any link-level address change. */
        ath9k_hw_setmac(ah, sc->sc_ah->macaddr);

        /* calculate and install multicast filter */
        mfilt[0] = mfilt[1] = ~0;
        ath9k_hw_setmcastfilter(ah, mfilt[0], mfilt[1]);
}

int ath_rx_init(struct ath_softc *sc, int nbufs)
{
        struct sk_buff *skb;
        struct ath_buf *bf;
        int error = 0;

        spin_lock_init(&sc->rx.rxflushlock);
        sc->sc_flags &= ~SC_OP_RXFLUSH;
        spin_lock_init(&sc->rx.rxbuflock);

        sc->rx.bufsize = roundup(IEEE80211_MAX_MPDU_LEN,
                                 min(sc->cachelsz, (u16)64));

        DPRINTF(sc, ATH_DBG_CONFIG, "cachelsz %u rxbufsize %u\n",
                sc->cachelsz, sc->rx.bufsize);

        /* Initialize rx descriptors */

        error = ath_descdma_setup(sc, &sc->rx.rxdma, &sc->rx.rxbuf,
                                  "rx", nbufs, 1);
        if (error != 0) {
                DPRINTF(sc, ATH_DBG_FATAL,
                        "failed to allocate rx descriptors: %d\n", error);
                goto err;
        }

        list_for_each_entry(bf, &sc->rx.rxbuf, list) {
                skb = ath_rxbuf_alloc(sc, sc->rx.bufsize, GFP_KERNEL);
                if (skb == NULL) {
                        error = -ENOMEM;
                        goto err;
                }

                bf->bf_mpdu = skb;
                bf->bf_buf_addr = dma_map_single(sc->dev, skb->data,
                                                 sc->rx.bufsize,
                                                 DMA_FROM_DEVICE);
                if (unlikely(dma_mapping_error(sc->dev,
                                               bf->bf_buf_addr))) {
                        dev_kfree_skb_any(skb);
                        bf->bf_mpdu = NULL;
                        DPRINTF(sc, ATH_DBG_FATAL,
                                "dma_mapping_error() on RX init\n");
                        error = -ENOMEM;
                        goto err;
                }
                bf->bf_dmacontext = bf->bf_buf_addr;
        }
        sc->rx.rxlink = NULL;

err:
        if (error)
                ath_rx_cleanup(sc);

        return error;
}

void ath_rx_cleanup(struct ath_softc *sc)
{
        struct sk_buff *skb;
        struct ath_buf *bf;

        list_for_each_entry(bf, &sc->rx.rxbuf, list) {
                skb = bf->bf_mpdu;
                if (skb) {
                        dma_unmap_single(sc->dev, bf->bf_buf_addr,
                                         sc->rx.bufsize, DMA_FROM_DEVICE);
                        dev_kfree_skb(skb);
                }
        }

        if (sc->rx.rxdma.dd_desc_len != 0)
                ath_descdma_cleanup(sc, &sc->rx.rxdma, &sc->rx.rxbuf);
}

/*
 * Calculate the receive filter according to the
 * operating mode and state:
 *
 * o always accept unicast, broadcast, and multicast traffic
 * o maintain current state of phy error reception (the hal
 *   may enable phy error frames for noise immunity work)
 * o probe request frames are accepted only when operating in
 *   hostap, adhoc, or monitor modes
 * o enable promiscuous mode according to the interface state
 * o accept beacons:
 *   - when operating in adhoc mode so the 802.11 layer creates
 *     node table entries for peers,
 *   - when operating in station mode for collecting rssi data when
 *     the station is otherwise quiet, or
 *   - when operating as a repeater so we see repeater-sta beacons
 *   - when scanning
 */

u32 ath_calcrxfilter(struct ath_softc *sc)
{
#define RX_FILTER_PRESERVE (ATH9K_RX_FILTER_PHYERR | ATH9K_RX_FILTER_PHYRADAR)

        u32 rfilt;

        rfilt = (ath9k_hw_getrxfilter(sc->sc_ah) & RX_FILTER_PRESERVE)
                | ATH9K_RX_FILTER_UCAST | ATH9K_RX_FILTER_BCAST
                | ATH9K_RX_FILTER_MCAST;

        /* If not a STA, enable processing of Probe Requests */
        if (sc->sc_ah->opmode != NL80211_IFTYPE_STATION)
                rfilt |= ATH9K_RX_FILTER_PROBEREQ;

        /*
         * Set promiscuous mode when FIF_PROMISC_IN_BSS is enabled for station
         * mode interface or when in monitor mode. AP mode does not need this
         * since it receives all in-BSS frames anyway.
         */
        if (((sc->sc_ah->opmode != NL80211_IFTYPE_AP) &&
             (sc->rx.rxfilter & FIF_PROMISC_IN_BSS)) ||
            (sc->sc_ah->opmode == NL80211_IFTYPE_MONITOR))
                rfilt |= ATH9K_RX_FILTER_PROM;

        if (sc->rx.rxfilter & FIF_CONTROL)
                rfilt |= ATH9K_RX_FILTER_CONTROL;

        if ((sc->sc_ah->opmode == NL80211_IFTYPE_STATION) &&
            !(sc->rx.rxfilter & FIF_BCN_PRBRESP_PROMISC))
                rfilt |= ATH9K_RX_FILTER_MYBEACON;
        else
                rfilt |= ATH9K_RX_FILTER_BEACON;

        /* If in HOSTAP mode, want to enable reception of PSPOLL frames */
        if (sc->sc_ah->opmode == NL80211_IFTYPE_AP)
                rfilt |= ATH9K_RX_FILTER_PSPOLL;

        if (sc->sec_wiphy) {
                /* TODO: only needed if more than one BSSID is in use in
                 * station/adhoc mode */
                /* TODO: for older chips, may need to add ATH9K_RX_FILTER_PROM
                 */
                rfilt |= ATH9K_RX_FILTER_MCAST_BCAST_ALL;
        }

        return rfilt;

#undef RX_FILTER_PRESERVE
}

int ath_startrecv(struct ath_softc *sc)
{
        struct ath_hw *ah = sc->sc_ah;
        struct ath_buf *bf, *tbf;

        spin_lock_bh(&sc->rx.rxbuflock);
        if (list_empty(&sc->rx.rxbuf))
                goto start_recv;

        sc->rx.rxlink = NULL;
        list_for_each_entry_safe(bf, tbf, &sc->rx.rxbuf, list) {
                ath_rx_buf_link(sc, bf);
        }

        /* We could have deleted elements so the list may be empty now */
        if (list_empty(&sc->rx.rxbuf))
                goto start_recv;

        bf = list_first_entry(&sc->rx.rxbuf, struct ath_buf, list);
        ath9k_hw_putrxbuf(ah, bf->bf_daddr);
        ath9k_hw_rxena(ah);

start_recv:
        spin_unlock_bh(&sc->rx.rxbuflock);
        ath_opmode_init(sc);
        ath9k_hw_startpcureceive(ah);

        return 0;
}

bool ath_stoprecv(struct ath_softc *sc)
{
        struct ath_hw *ah = sc->sc_ah;
        bool stopped;

        ath9k_hw_stoppcurecv(ah);
        ath9k_hw_setrxfilter(ah, 0);
        stopped = ath9k_hw_stopdmarecv(ah);
        sc->rx.rxlink = NULL;

        return stopped;
}

void ath_flushrecv(struct ath_softc *sc)
{
        spin_lock_bh(&sc->rx.rxflushlock);
        sc->sc_flags |= SC_OP_RXFLUSH;
        ath_rx_tasklet(sc, 1);
        sc->sc_flags &= ~SC_OP_RXFLUSH;
        spin_unlock_bh(&sc->rx.rxflushlock);
}

static bool ath_beacon_dtim_pending_cab(struct sk_buff *skb)
{
        /* Check whether the Beacon frame has DTIM indicating buffered bc/mc */
        struct ieee80211_mgmt *mgmt;
        u8 *pos, *end, id, elen;
        struct ieee80211_tim_ie *tim;

        mgmt = (struct ieee80211_mgmt *)skb->data;
        pos = mgmt->u.beacon.variable;
        end = skb->data + skb->len;

        while (pos + 2 < end) {
                id = *pos++;
                elen = *pos++;
                if (pos + elen > end)
                        break;

                if (id == WLAN_EID_TIM) {
                        if (elen < sizeof(*tim))
                                break;
                        tim = (struct ieee80211_tim_ie *) pos;
                        if (tim->dtim_count != 0)
                                break;
                        return tim->bitmap_ctrl & 0x01;
                }

                pos += elen;
        }

        return false;
}

static void ath_rx_ps_back_to_sleep(struct ath_softc *sc)
{
        sc->sc_flags &= ~(SC_OP_WAIT_FOR_BEACON | SC_OP_WAIT_FOR_CAB);
}

static void ath_rx_ps_beacon(struct ath_softc *sc, struct sk_buff *skb)
{
        struct ieee80211_mgmt *mgmt;

        if (skb->len < 24 + 8 + 2 + 2)
                return;

        mgmt = (struct ieee80211_mgmt *)skb->data;
        if (memcmp(sc->curbssid, mgmt->bssid, ETH_ALEN) != 0)
                return; /* not from our current AP */

        if (sc->sc_flags & SC_OP_BEACON_SYNC) {
                sc->sc_flags &= ~SC_OP_BEACON_SYNC;
                DPRINTF(sc, ATH_DBG_PS, "Reconfigure Beacon timers based on "
                        "timestamp from the AP\n");
                ath_beacon_config(sc, NULL);
        }

        if (!(sc->hw->conf.flags & IEEE80211_CONF_PS)) {
                /* We are not in PS mode anymore; remain awake */
                DPRINTF(sc, ATH_DBG_PS, "Not in PS mode anymore, remain "
                        "awake\n");
                sc->sc_flags &= ~(SC_OP_WAIT_FOR_BEACON | SC_OP_WAIT_FOR_CAB);
                return;
        }

        if (ath_beacon_dtim_pending_cab(skb)) {
                /*
                 * Remain awake waiting for buffered broadcast/multicast
                 * frames. If the last broadcast/multicast frame is not
                 * received properly, the next beacon frame will work as
                 * a backup trigger for returning into NETWORK SLEEP state,
                 * so we are waiting for it as well.
                 */
                DPRINTF(sc, ATH_DBG_PS, "Received DTIM beacon indicating "
                        "buffered broadcast/multicast frame(s)\n");
                sc->sc_flags |= SC_OP_WAIT_FOR_CAB | SC_OP_WAIT_FOR_BEACON;
                return;
        }

        if (sc->sc_flags & SC_OP_WAIT_FOR_CAB) {
                /*
                 * This can happen if a broadcast frame is dropped or the AP
                 * fails to send a frame indicating that all CAB frames have
                 * been delivered.
                 */
                DPRINTF(sc, ATH_DBG_PS, "PS wait for CAB frames timed out\n");
        }

        /* No more broadcast/multicast frames to be received at this point. */
        ath_rx_ps_back_to_sleep(sc);
}

static void ath_rx_ps(struct ath_softc *sc, struct sk_buff *skb)
{
        struct ieee80211_hdr *hdr;

        hdr = (struct ieee80211_hdr *)skb->data;

        /* Process Beacon and CAB receive in PS state */
        if ((sc->sc_flags & SC_OP_WAIT_FOR_BEACON) &&
            ieee80211_is_beacon(hdr->frame_control))
                ath_rx_ps_beacon(sc, skb);
        else if ((sc->sc_flags & SC_OP_WAIT_FOR_CAB) &&
                 (ieee80211_is_data(hdr->frame_control) ||
                  ieee80211_is_action(hdr->frame_control)) &&
                 is_multicast_ether_addr(hdr->addr1) &&
                 !ieee80211_has_moredata(hdr->frame_control)) {
                DPRINTF(sc, ATH_DBG_PS, "All PS CAB frames received, back to "
                        "sleep\n");
                /*
                 * No more broadcast/multicast frames to be received at this
                 * point.
                 */
                ath_rx_ps_back_to_sleep(sc);
        } else if ((sc->sc_flags & SC_OP_WAIT_FOR_PSPOLL_DATA) &&
                   !is_multicast_ether_addr(hdr->addr1) &&
                   !ieee80211_has_morefrags(hdr->frame_control)) {
                sc->sc_flags &= ~SC_OP_WAIT_FOR_PSPOLL_DATA;
                DPRINTF(sc, ATH_DBG_PS, "Going back to sleep after having "
                        "received PS-Poll data (0x%x)\n",
                        sc->sc_flags & (SC_OP_WAIT_FOR_BEACON |
                                        SC_OP_WAIT_FOR_CAB |
                                        SC_OP_WAIT_FOR_PSPOLL_DATA |
                                        SC_OP_WAIT_FOR_TX_ACK));
        }
}

static void ath_rx_send_to_mac80211(struct ath_softc *sc, struct sk_buff *skb,
                                    struct ieee80211_rx_status *rx_status)
{
        struct ieee80211_hdr *hdr;

        hdr = (struct ieee80211_hdr *)skb->data;

        /* Send the frame to mac80211 */
        if (is_multicast_ether_addr(hdr->addr1)) {
                int i;
                /*
                 * Deliver broadcast/multicast frames to all suitable
                 * virtual wiphys.
                 */
                /* TODO: filter based on channel configuration */
                for (i = 0; i < sc->num_sec_wiphy; i++) {
                        struct ath_wiphy *aphy = sc->sec_wiphy[i];
                        struct sk_buff *nskb;
                        if (aphy == NULL)
                                continue;
                        nskb = skb_copy(skb, GFP_ATOMIC);
                        if (nskb) {
                                memcpy(IEEE80211_SKB_RXCB(nskb), rx_status,
                                        sizeof(*rx_status));
                                ieee80211_rx(aphy->hw, nskb);
                        }
                }
                memcpy(IEEE80211_SKB_RXCB(skb), rx_status, sizeof(*rx_status));
                ieee80211_rx(sc->hw, skb);
        } else {
                /* Deliver unicast frames based on receiver address */
                memcpy(IEEE80211_SKB_RXCB(skb), rx_status, sizeof(*rx_status));
                ieee80211_rx(ath_get_virt_hw(sc, hdr), skb);
        }
}

int ath_rx_tasklet(struct ath_softc *sc, int flush)
{
#define PA2DESC(_sc, _pa)                                               \
        ((struct ath_desc *)((caddr_t)(_sc)->rx.rxdma.dd_desc +         \
                             ((_pa) - (_sc)->rx.rxdma.dd_desc_paddr)))

        struct ath_buf *bf;
        struct ath_desc *ds;
        struct sk_buff *skb = NULL, *requeue_skb;
        struct ieee80211_rx_status rx_status;
        struct ath_hw *ah = sc->sc_ah;
        struct ieee80211_hdr *hdr;
        int hdrlen, padsize, retval;
        bool decrypt_error = false;
        u8 keyix;
        __le16 fc;

        spin_lock_bh(&sc->rx.rxbuflock);

        do {
                /* If handling rx interrupt and flush is in progress => exit */
                if ((sc->sc_flags & SC_OP_RXFLUSH) && (flush == 0))
                        break;

                if (list_empty(&sc->rx.rxbuf)) {
                        sc->rx.rxlink = NULL;
                        break;
                }

                bf = list_first_entry(&sc->rx.rxbuf, struct ath_buf, list);
                ds = bf->bf_desc;

                /*
                 * Must provide the virtual address of the current
                 * descriptor, the physical address, and the virtual
                 * address of the next descriptor in the h/w chain.
                 * This allows the HAL to look ahead to see if the
                 * hardware is done with a descriptor by checking the
                 * done bit in the following descriptor and the address
                 * of the current descriptor the DMA engine is working
                 * on.  All this is necessary because of our use of
                 * a self-linked list to avoid rx overruns.
                 */
                retval = ath9k_hw_rxprocdesc(ah, ds,
                                             bf->bf_daddr,
                                             PA2DESC(sc, ds->ds_link),
                                             0);
                if (retval == -EINPROGRESS) {
                        struct ath_buf *tbf;
                        struct ath_desc *tds;

                        if (list_is_last(&bf->list, &sc->rx.rxbuf)) {
                                sc->rx.rxlink = NULL;
                                break;
                        }

                        tbf = list_entry(bf->list.next, struct ath_buf, list);

                        /*
                         * On some hardware the descriptor status words could
                         * get corrupted, including the done bit. Because of
                         * this, check if the next descriptor's done bit is
                         * set or not.
                         *
                         * If the next descriptor's done bit is set, the current
                         * descriptor has been corrupted. Force s/w to discard
                         * this descriptor and continue...
                         */

                        tds = tbf->bf_desc;
                        retval = ath9k_hw_rxprocdesc(ah, tds, tbf->bf_daddr,
                                             PA2DESC(sc, tds->ds_link), 0);
                        if (retval == -EINPROGRESS) {
                                break;
                        }
                }

                skb = bf->bf_mpdu;
                if (!skb)
                        continue;

                /*
                 * Synchronize the DMA transfer with CPU before
                 * 1. accessing the frame
                 * 2. requeueing the same buffer to h/w
                 */
                dma_sync_single_for_cpu(sc->dev, bf->bf_buf_addr,
                                sc->rx.bufsize,
                                DMA_FROM_DEVICE);

                /*
                 * If we're asked to flush receive queue, directly
                 * chain it back at the queue without processing it.
                 */
                if (flush)
                        goto requeue;

                if (!ds->ds_rxstat.rs_datalen)
                        goto requeue;

                /* The status portion of the descriptor could get corrupted. */
                if (sc->rx.bufsize < ds->ds_rxstat.rs_datalen)
                        goto requeue;

                if (!ath_rx_prepare(skb, ds, &rx_status, &decrypt_error, sc))
                        goto requeue;

                /* Ensure we always have an skb to requeue once we are done
                 * processing the current buffer's skb */
                requeue_skb = ath_rxbuf_alloc(sc, sc->rx.bufsize, GFP_ATOMIC);

                /* If there is no memory we ignore the current RX'd frame,
                 * tell hardware it can give us a new frame using the old
                 * skb and put it at the tail of the sc->rx.rxbuf list for
                 * processing. */
                if (!requeue_skb)
                        goto requeue;

                /* Unmap the frame */
                dma_unmap_single(sc->dev, bf->bf_buf_addr,
                                 sc->rx.bufsize,
                                 DMA_FROM_DEVICE);

                skb_put(skb, ds->ds_rxstat.rs_datalen);
                skb->protocol = cpu_to_be16(ETH_P_CONTROL);

                /* see if any padding is done by the hw and remove it */
                hdr = (struct ieee80211_hdr *)skb->data;
                hdrlen = ieee80211_get_hdrlen_from_skb(skb);
                fc = hdr->frame_control;

                /* The MAC header is padded to have 32-bit boundary if the
                 * packet payload is non-zero. The general calculation for
                 * padsize would take into account odd header lengths:
                 * padsize = (4 - hdrlen % 4) % 4; However, since only
                 * even-length headers are used, padding can only be 0 or 2
                 * bytes and we can optimize this a bit. In addition, we must
                 * not try to remove padding from short control frames that do
                 * not have payload. */
                padsize = hdrlen & 3;
                if (padsize && hdrlen >= 24) {
                        memmove(skb->data + padsize, skb->data, hdrlen);
                        skb_pull(skb, padsize);
                }

                keyix = ds->ds_rxstat.rs_keyix;

                if (!(keyix == ATH9K_RXKEYIX_INVALID) && !decrypt_error) {
                        rx_status.flag |= RX_FLAG_DECRYPTED;
                } else if (ieee80211_has_protected(fc)
                           && !decrypt_error && skb->len >= hdrlen + 4) {
                        keyix = skb->data[hdrlen + 3] >> 6;

                        if (test_bit(keyix, sc->keymap))
                                rx_status.flag |= RX_FLAG_DECRYPTED;
                }
                if (ah->sw_mgmt_crypto &&
                    (rx_status.flag & RX_FLAG_DECRYPTED) &&
                    ieee80211_is_mgmt(fc)) {
                        /* Use software decrypt for management frames. */
                        rx_status.flag &= ~RX_FLAG_DECRYPTED;
                }

                /* We will now give hardware our shiny new allocated skb */
                bf->bf_mpdu = requeue_skb;
                bf->bf_buf_addr = dma_map_single(sc->dev, requeue_skb->data,
                                         sc->rx.bufsize,
                                         DMA_FROM_DEVICE);
                if (unlikely(dma_mapping_error(sc->dev,
                          bf->bf_buf_addr))) {
                        dev_kfree_skb_any(requeue_skb);
                        bf->bf_mpdu = NULL;
                        DPRINTF(sc, ATH_DBG_FATAL,
                                "dma_mapping_error() on RX\n");
                        ath_rx_send_to_mac80211(sc, skb, &rx_status);
                        break;
                }
                bf->bf_dmacontext = bf->bf_buf_addr;

                /*
                 * change the default rx antenna if rx diversity chooses the
                 * other antenna 3 times in a row.
                 */
                if (sc->rx.defant != ds->ds_rxstat.rs_antenna) {
                        if (++sc->rx.rxotherant >= 3)
                                ath_setdefantenna(sc, ds->ds_rxstat.rs_antenna);
                } else {
                        sc->rx.rxotherant = 0;
                }

                if (unlikely(sc->sc_flags & (SC_OP_WAIT_FOR_BEACON |
                                             SC_OP_WAIT_FOR_CAB |
                                             SC_OP_WAIT_FOR_PSPOLL_DATA)))
                        ath_rx_ps(sc, skb);

                ath_rx_send_to_mac80211(sc, skb, &rx_status);

requeue:
                list_move_tail(&bf->list, &sc->rx.rxbuf);
                ath_rx_buf_link(sc, bf);
        } while (1);

        spin_unlock_bh(&sc->rx.rxbuflock);

        return 0;
#undef PA2DESC
}