freebsd-skq/sys/dev/ath/if_ath_tx_edma.c

/*-
 * Copyright (c) 2012 Adrian Chadd <adrian@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer,
 *    without modification.
 * 2. Redistributions in binary form must reproduce at minimum a disclaimer
 *    similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
 *    redistribution must be conditioned upon including a substantially
 *    similar Disclaimer requirement for further binary redistribution.
 *
 * NO WARRANTY
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
 * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGES.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

/*
 * Driver for the Atheros Wireless LAN controller.
 *
 * This software is derived from work of Atsushi Onoe; his contribution
 * is greatly appreciated.
 */

#include "opt_inet.h"
#include "opt_ath.h"
/*
 * This is needed for register operations which are performed
 * by the driver - eg, calls to ath_hal_gettsf32().
 *
 * It's also required for any AH_DEBUG checks in here, eg the
 * module dependencies.
 */
#include "opt_ah.h"
#include "opt_wlan.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysctl.h>
#include <sys/mbuf.h>
#include <sys/malloc.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/kernel.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/errno.h>
#include <sys/callout.h>
#include <sys/bus.h>
#include <sys/endian.h>
#include <sys/kthread.h>
#include <sys/taskqueue.h>
#include <sys/priv.h>
#include <sys/module.h>
#include <sys/ktr.h>
#include <sys/smp.h>	/* for mp_ncpus */

#include <machine/bus.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/if_media.h>
#include <net/if_types.h>
#include <net/if_arp.h>
#include <net/ethernet.h>
#include <net/if_llc.h>

#include <net80211/ieee80211_var.h>
#include <net80211/ieee80211_regdomain.h>
#ifdef IEEE80211_SUPPORT_SUPERG
#include <net80211/ieee80211_superg.h>
#endif
#ifdef IEEE80211_SUPPORT_TDMA
#include <net80211/ieee80211_tdma.h>
#endif

#include <net/bpf.h>

#ifdef INET
#include <netinet/in.h>
#include <netinet/if_ether.h>
#endif

#include <dev/ath/if_athvar.h>
#include <dev/ath/ath_hal/ah_devid.h>		/* XXX for softled */
#include <dev/ath/ath_hal/ah_diagcodes.h>

#include <dev/ath/if_ath_debug.h>
#include <dev/ath/if_ath_misc.h>
#include <dev/ath/if_ath_tsf.h>
#include <dev/ath/if_ath_tx.h>
#include <dev/ath/if_ath_sysctl.h>
#include <dev/ath/if_ath_led.h>
#include <dev/ath/if_ath_keycache.h>
#include <dev/ath/if_ath_rx.h>
#include <dev/ath/if_ath_beacon.h>
#include <dev/ath/if_athdfs.h>

#ifdef ATH_TX99_DIAG
#include <dev/ath/ath_tx99/ath_tx99.h>
#endif

#include <dev/ath/if_ath_tx_edma.h>

#ifdef	ATH_DEBUG_ALQ
#include <dev/ath/if_ath_alq.h>
#endif

/*
 * some general macros
 */
#define	INCR(_l, _sz)		(_l) ++; (_l) &= ((_sz) - 1)
#define	DECR(_l, _sz)		(_l) --; (_l) &= ((_sz) - 1)

/*
 * XXX doesn't belong here, and should be tunable
 */
#define	ATH_TXSTATUS_RING_SIZE	512

MALLOC_DECLARE(M_ATHDEV);

static void ath_edma_tx_processq(struct ath_softc *sc, int dosched);

static void
ath_edma_tx_fifo_fill(struct ath_softc *sc, struct ath_txq *txq)
{
	struct ath_buf *bf;
	int i = 0;

	ATH_TXQ_LOCK_ASSERT(txq);

	DPRINTF(sc, ATH_DEBUG_TX_PROC, "%s: called\n", __func__);

	TAILQ_FOREACH(bf, &txq->axq_q, bf_list) {
		if (txq->axq_fifo_depth >= HAL_TXFIFO_DEPTH)
			break;
		ath_hal_puttxbuf(sc->sc_ah, txq->axq_qnum, bf->bf_daddr);
#ifdef	ATH_DEBUG
		if (sc->sc_debug & ATH_DEBUG_XMIT_DESC)
			ath_printtxbuf(sc, bf, txq->axq_qnum, i, 0);
#endif/* ATH_DEBUG */
#ifdef	ATH_DEBUG_ALQ
		if (if_ath_alq_checkdebug(&sc->sc_alq, ATH_ALQ_EDMA_TXDESC))
			ath_tx_alq_post(sc, bf);
#endif /* ATH_DEBUG_ALQ */
		txq->axq_fifo_depth++;
		i++;
	}
	if (i > 0)
		ath_hal_txstart(sc->sc_ah, txq->axq_qnum);
}

/*
 * Re-initialise the DMA FIFO with the current contents of
 * said TXQ.
 *
 * This should only be called as part of the chip reset path, as it
 * assumes the FIFO is currently empty.
 */
static void
ath_edma_dma_restart(struct ath_softc *sc, struct ath_txq *txq)
{

	DPRINTF(sc, ATH_DEBUG_RESET, "%s: called: txq=%p, qnum=%d\n",
	    __func__,
	    txq,
	    txq->axq_qnum);

	ATH_TXQ_LOCK_ASSERT(txq);
	ath_edma_tx_fifo_fill(sc, txq);

}

/*
 * Hand off this frame to a hardware queue.
 *
 * Things are a bit hairy in the EDMA world.  The TX FIFO is only
 * 8 entries deep, so we need to keep track of exactly what we've
 * pushed into the FIFO and what's just sitting in the TX queue,
 * waiting to go out.
 *
 * So this is split into two halves - frames get appended to the
 * TXQ; then a scheduler is called to push some frames into the
 * actual TX FIFO.
 */
static void
ath_edma_xmit_handoff_hw(struct ath_softc *sc, struct ath_txq *txq,
    struct ath_buf *bf)
{
	struct ath_hal *ah = sc->sc_ah;

	ATH_TXQ_LOCK_ASSERT(txq);

	KASSERT((bf->bf_flags & ATH_BUF_BUSY) == 0,
	    ("%s: busy status 0x%x", __func__, bf->bf_flags));

	/*
	 * XXX TODO: write a hard-coded check to ensure that
	 * the queue id in the TX descriptor matches txq->axq_qnum.
	 */

	/* Update aggr stats */
	if (bf->bf_state.bfs_aggr)
		txq->axq_aggr_depth++;

	/* Push and update frame stats */
	ATH_TXQ_INSERT_TAIL(txq, bf, bf_list);

	/* Only schedule to the FIFO if there's space */
	if (txq->axq_fifo_depth < HAL_TXFIFO_DEPTH) {
#ifdef	ATH_DEBUG
		if (sc->sc_debug & ATH_DEBUG_XMIT_DESC)
			ath_printtxbuf(sc, bf, txq->axq_qnum, 0, 0);
#endif /* ATH_DEBUG */
#ifdef	ATH_DEBUG_ALQ
		if (if_ath_alq_checkdebug(&sc->sc_alq, ATH_ALQ_EDMA_TXDESC))
			ath_tx_alq_post(sc, bf);
#endif	/* ATH_DEBUG_ALQ */
		ath_hal_puttxbuf(ah, txq->axq_qnum, bf->bf_daddr);
		txq->axq_fifo_depth++;
		ath_hal_txstart(ah, txq->axq_qnum);
	}
}

/*
 * Hand off this frame to a multicast software queue.
 *
 * The EDMA TX CABQ will get a list of chained frames, chained
 * together using the next pointer.  The single head of that
 * particular queue is pushed to the hardware CABQ.
 */
static void
ath_edma_xmit_handoff_mcast(struct ath_softc *sc, struct ath_txq *txq,
    struct ath_buf *bf)
{

	ATH_TXQ_LOCK_ASSERT(txq);
	KASSERT((bf->bf_flags & ATH_BUF_BUSY) == 0,
	    ("%s: busy status 0x%x", __func__, bf->bf_flags));

	/*
	 * XXX this is mostly duplicated in ath_tx_handoff_mcast().
	 */
	if (ATH_TXQ_FIRST(txq) != NULL) {
		struct ath_buf *bf_last = ATH_TXQ_LAST(txq, axq_q_s);
		struct ieee80211_frame *wh;

		/* mark previous frame */
		wh = mtod(bf_last->bf_m, struct ieee80211_frame *);
		wh->i_fc[1] |= IEEE80211_FC1_MORE_DATA;

		/* sync descriptor to memory */
		bus_dmamap_sync(sc->sc_dmat, bf_last->bf_dmamap,
		   BUS_DMASYNC_PREWRITE);
	}

#ifdef	ATH_DEBUG_ALQ
	if (if_ath_alq_checkdebug(&sc->sc_alq, ATH_ALQ_EDMA_TXDESC))
		ath_tx_alq_post(sc, bf);
#endif	/* ATH_DEBUG_ALQ */

	ATH_TXQ_INSERT_TAIL(txq, bf, bf_list);
	ath_hal_gettxdesclinkptr(sc->sc_ah, bf->bf_lastds, &txq->axq_link);
}

/*
 * Handoff this frame to the hardware.
 *
 * For the multicast queue, this will treat it as a software queue
 * and append it to the list, after updating the MORE_DATA flag
 * in the previous frame.  The cabq processing code will ensure
 * that the queue contents gets transferred over.
 *
 * For the hardware queues, this will queue a frame to the queue
 * like before, then populate the FIFO from that.  Since the
 * EDMA hardware has 8 FIFO slots per TXQ, this ensures that
 * frames such as management frames don't get prematurely dropped.
 *
 * This does imply that a similar flush-hwq-to-fifoq method will
 * need to be called from the processq function, before the
 * per-node software scheduler is called.
 */
static void
ath_edma_xmit_handoff(struct ath_softc *sc, struct ath_txq *txq,
    struct ath_buf *bf)
{

	ATH_TXQ_LOCK_ASSERT(txq);

	DPRINTF(sc, ATH_DEBUG_XMIT_DESC,
	    "%s: called; bf=%p, txq=%p, qnum=%d\n",
	    __func__,
	    bf,
	    txq,
	    txq->axq_qnum);

	if (txq->axq_qnum == ATH_TXQ_SWQ)
		ath_edma_xmit_handoff_mcast(sc, txq, bf);
	else
		ath_edma_xmit_handoff_hw(sc, txq, bf);

#if 0
	/*
	 * XXX For now this is a placeholder; free the buffer
	 * and inform the stack that the TX failed.
	 */
	ath_tx_default_comp(sc, bf, 1);
#endif
}

static int
ath_edma_setup_txfifo(struct ath_softc *sc, int qnum)
{
	struct ath_tx_edma_fifo *te = &sc->sc_txedma[qnum];

	te->m_fifo = malloc(sizeof(struct ath_buf *) * HAL_TXFIFO_DEPTH,
	    M_ATHDEV,
	    M_NOWAIT | M_ZERO);
	if (te->m_fifo == NULL) {
		device_printf(sc->sc_dev, "%s: malloc failed\n",
		    __func__);
		return (-ENOMEM);
	}

	/*
	 * Set initial "empty" state.
	 */
	te->m_fifo_head = te->m_fifo_tail = te->m_fifo_depth = 0;
	
	return (0);
}

static int
ath_edma_free_txfifo(struct ath_softc *sc, int qnum)
{
	struct ath_tx_edma_fifo *te = &sc->sc_txedma[qnum];

	/* XXX TODO: actually deref the ath_buf entries? */
	free(te->m_fifo, M_ATHDEV);
	return (0);
}

static int
ath_edma_dma_txsetup(struct ath_softc *sc)
{
	int error;
	int i;

	error = ath_descdma_alloc_desc(sc, &sc->sc_txsdma,
	    NULL, "txcomp", sc->sc_tx_statuslen, ATH_TXSTATUS_RING_SIZE);
	if (error != 0)
		return (error);

	ath_hal_setuptxstatusring(sc->sc_ah,
	    (void *) sc->sc_txsdma.dd_desc,
	    sc->sc_txsdma.dd_desc_paddr,
	    ATH_TXSTATUS_RING_SIZE);

	for (i = 0; i < HAL_NUM_TX_QUEUES; i++) {
		ath_edma_setup_txfifo(sc, i);
	}

	return (0);
}

static int
ath_edma_dma_txteardown(struct ath_softc *sc)
{
	int i;

	for (i = 0; i < HAL_NUM_TX_QUEUES; i++) {
		ath_edma_free_txfifo(sc, i);
	}

	ath_descdma_cleanup(sc, &sc->sc_txsdma, NULL);
	return (0);
}

/*
 * Drain all TXQs, potentially after completing the existing completed
 * frames.
 */
static void
ath_edma_tx_drain(struct ath_softc *sc, ATH_RESET_TYPE reset_type)
{
	struct ifnet *ifp = sc->sc_ifp;
	int i;

	DPRINTF(sc, ATH_DEBUG_RESET, "%s: called\n", __func__);

	(void) ath_stoptxdma(sc);

	/*
	 * If reset type is noloss, the TX FIFO needs to be serviced
	 * and those frames need to be handled.
	 *
	 * Otherwise, just toss everything in each TX queue.
	 */
	if (reset_type == ATH_RESET_NOLOSS) {
		ath_edma_tx_processq(sc, 0);
	} else {
		for (i = 0; i < HAL_NUM_TX_QUEUES; i++) {
			if (ATH_TXQ_SETUP(sc, i))
				ath_tx_draintxq(sc, &sc->sc_txq[i]);
		}
	}

	/* XXX dump out the TX completion FIFO contents */

	/* XXX dump out the frames */

	IF_LOCK(&ifp->if_snd);
	ifp->if_drv_flags &= ~IFF_DRV_OACTIVE;
	IF_UNLOCK(&ifp->if_snd);
	sc->sc_wd_timer = 0;
}

/*
 * TX completion tasklet.
 */

static void
ath_edma_tx_proc(void *arg, int npending)
{
	struct ath_softc *sc = (struct ath_softc *) arg;

	DPRINTF(sc, ATH_DEBUG_TX_PROC, "%s: called, npending=%d\n",
	    __func__, npending);
	ath_edma_tx_processq(sc, 1);
}

/*
 * Process the TX status queue.
 */
static void
ath_edma_tx_processq(struct ath_softc *sc, int dosched)
{
	struct ath_hal *ah = sc->sc_ah;
	HAL_STATUS status;
	struct ath_tx_status ts;
	struct ath_txq *txq;
	struct ath_buf *bf;
	struct ieee80211_node *ni;
	int nacked = 0;
	int idx;

#ifdef	ATH_DEBUG
	/* XXX */
	uint32_t txstatus[32];
#endif

	for (idx = 0; ; idx++) {
		bzero(&ts, sizeof(ts));

		ATH_TXSTATUS_LOCK(sc);
#ifdef	ATH_DEBUG
		ath_hal_gettxrawtxdesc(ah, txstatus);
#endif
		status = ath_hal_txprocdesc(ah, NULL, (void *) &ts);
		ATH_TXSTATUS_UNLOCK(sc);

#ifdef	ATH_DEBUG
		if (sc->sc_debug & ATH_DEBUG_TX_PROC)
			ath_printtxstatbuf(sc, NULL, txstatus, ts.ts_queue_id,
			    idx, (status == HAL_OK));
#endif

		if (status == HAL_EINPROGRESS)
			break;

		/*
		 * If there is an error with this descriptor, continue
		 * processing.
		 *
		 * XXX TBD: log some statistics?
		 */
		if (status == HAL_EIO) {
			device_printf(sc->sc_dev, "%s: invalid TX status?\n",
			    __func__);
			continue;
		}

#ifdef	ATH_DEBUG_ALQ
		if (if_ath_alq_checkdebug(&sc->sc_alq, ATH_ALQ_EDMA_TXSTATUS))
			if_ath_alq_post(&sc->sc_alq, ATH_ALQ_EDMA_TXSTATUS,
			    sc->sc_tx_statuslen,
			    (char *) txstatus);
#endif /* ATH_DEBUG_ALQ */

		/*
		 * At this point we have a valid status descriptor.
		 * The QID and descriptor ID (which currently isn't set)
		 * is part of the status.
		 *
		 * We then assume that the descriptor in question is the
		 * -head- of the given QID.  Eventually we should verify
		 * this by using the descriptor ID.
		 */

		/*
		 * The beacon queue is not currently a "real" queue.
		 * Frames aren't pushed onto it and the lock isn't setup.
		 * So skip it for now; the beacon handling code will
		 * free and alloc more beacon buffers as appropriate.
		 */
		if (ts.ts_queue_id == sc->sc_bhalq)
			continue;

		txq = &sc->sc_txq[ts.ts_queue_id];

		ATH_TXQ_LOCK(txq);
		bf = TAILQ_FIRST(&txq->axq_q);

		DPRINTF(sc, ATH_DEBUG_TX_PROC, "%s: qcuid=%d, bf=%p\n",
		    __func__,
		    ts.ts_queue_id, bf);

		/* XXX TODO: actually output debugging info about this */

#if 0
		/* XXX assert the buffer/descriptor matches the status descid */
		if (ts.ts_desc_id != bf->bf_descid) {
			device_printf(sc->sc_dev,
			    "%s: mismatched descid (qid=%d, tsdescid=%d, "
			    "bfdescid=%d\n",
			    __func__,
			    ts.ts_queue_id,
			    ts.ts_desc_id,
			    bf->bf_descid);
		}
#endif

		/* This removes the buffer and decrements the queue depth */
		ATH_TXQ_REMOVE(txq, bf, bf_list);
		if (bf->bf_state.bfs_aggr)
			txq->axq_aggr_depth--;
		txq->axq_fifo_depth --;
		/* XXX assert FIFO depth >= 0 */
		ATH_TXQ_UNLOCK(txq);

		/*
		 * First we need to make sure ts_rate is valid.
		 *
		 * Pre-EDMA chips pass the whole TX descriptor to
		 * the proctxdesc function which will then fill out
		 * ts_rate based on the ts_finaltsi (final TX index)
		 * in the TX descriptor.  However the TX completion
		 * FIFO doesn't have this information.  So here we
		 * do a separate HAL call to populate that information.
		 *
		 * The same problem exists with ts_longretry.
		 * The FreeBSD HAL corrects ts_longretry in the HAL layer;
		 * the AR9380 HAL currently doesn't.  So until the HAL
		 * is imported and this can be added, we correct for it
		 * here.
		 */
		/* XXX TODO */
		/* XXX faked for now. Ew. */
		if (ts.ts_finaltsi < 4) {
			ts.ts_rate =
			    bf->bf_state.bfs_rc[ts.ts_finaltsi].ratecode;
			switch (ts.ts_finaltsi) {
			case 3: ts.ts_longretry +=
			    bf->bf_state.bfs_rc[2].tries;
			case 2: ts.ts_longretry +=
			    bf->bf_state.bfs_rc[1].tries;
			case 1: ts.ts_longretry +=
			    bf->bf_state.bfs_rc[0].tries;
			}
		} else {
			device_printf(sc->sc_dev, "%s: finaltsi=%d\n",
			    __func__,
			    ts.ts_finaltsi);
			ts.ts_rate = bf->bf_state.bfs_rc[0].ratecode;
		}

		/*
		 * XXX This is terrible.
		 *
		 * Right now, some code uses the TX status that is
		 * passed in here, but the completion handlers in the
		 * software TX path also use bf_status.ds_txstat.
		 * Ew.  That should all go away.
		 *
		 * XXX It's also possible the rate control completion
		 * routine is called twice.
		 */
		memcpy(&bf->bf_status, &ts, sizeof(ts));

		ni = bf->bf_node;

		/* Update RSSI */
		/* XXX duplicate from ath_tx_processq */
		if (ni != NULL && ts.ts_status == 0 &&
		    ((bf->bf_state.bfs_txflags & HAL_TXDESC_NOACK) == 0)) {
			nacked++;
			sc->sc_stats.ast_tx_rssi = ts.ts_rssi;
			ATH_RSSI_LPF(sc->sc_halstats.ns_avgtxrssi,
			    ts.ts_rssi);
		}

		/* Handle frame completion and rate control update */
		ath_tx_process_buf_completion(sc, txq, &ts, bf);

		/* bf is invalid at this point */

		/*
		 * Now that there's space in the FIFO, let's push some
		 * more frames into it.
		 *
		 * Unfortunately for now, the txq has FIFO and non-FIFO
		 * frames in the same linked list, so there's no way
		 * to quickly/easily populate frames without walking
		 * the queue and skipping 'axq_fifo_depth' frames.
		 *
		 * So for now, let's only repopulate the FIFO once it
		 * is empty.  It's sucky for performance but it's enough
		 * to begin validating that things are somewhat
		 * working.
		 */
		ATH_TXQ_LOCK(txq);
		if (dosched && txq->axq_fifo_depth == 0) {
			ath_edma_tx_fifo_fill(sc, txq);
		}
		ATH_TXQ_UNLOCK(txq);
	}

	sc->sc_wd_timer = 0;

	if (idx > 0) {
		IF_LOCK(&sc->sc_ifp->if_snd);
		sc->sc_ifp->if_drv_flags &= ~IFF_DRV_OACTIVE;
		IF_UNLOCK(&sc->sc_ifp->if_snd);
	}

	/* Kick software scheduler */
	/*
	 * XXX It's inefficient to do this if the FIFO queue is full,
	 * but there's no easy way right now to only populate
	 * the txq task for _one_ TXQ.  This should be fixed.
	 */
	if (dosched)
		taskqueue_enqueue(sc->sc_tq, &sc->sc_txqtask);
}

static void
ath_edma_attach_comp_func(struct ath_softc *sc)
{

	TASK_INIT(&sc->sc_txtask, 0, ath_edma_tx_proc, sc);
}

void
ath_xmit_setup_edma(struct ath_softc *sc)
{

	/* Fetch EDMA field and buffer sizes */
	(void) ath_hal_gettxdesclen(sc->sc_ah, &sc->sc_tx_desclen);
	(void) ath_hal_gettxstatuslen(sc->sc_ah, &sc->sc_tx_statuslen);
	(void) ath_hal_getntxmaps(sc->sc_ah, &sc->sc_tx_nmaps);

	device_printf(sc->sc_dev, "TX descriptor length: %d\n",
	    sc->sc_tx_desclen);
	device_printf(sc->sc_dev, "TX status length: %d\n",
	    sc->sc_tx_statuslen);
	device_printf(sc->sc_dev, "TX buffers per descriptor: %d\n",
	    sc->sc_tx_nmaps);

	sc->sc_tx.xmit_setup = ath_edma_dma_txsetup;
	sc->sc_tx.xmit_teardown = ath_edma_dma_txteardown;
	sc->sc_tx.xmit_attach_comp_func = ath_edma_attach_comp_func;

	sc->sc_tx.xmit_dma_restart = ath_edma_dma_restart;
	sc->sc_tx.xmit_handoff = ath_edma_xmit_handoff;
	sc->sc_tx.xmit_drain = ath_edma_tx_drain;
}