ath9k: unify edma and non-edma tx code, improve tx fifo handling

EDMA based chips (AR9380+) have 8 Tx FIFO slots, which are used to fix the
tx queue start/stop race conditions which have to be worked around for
earlier chips by keeping the last descriptor in the queue. The current code
stores all frames that do not fit onto the 8 FIFO slots in a separate
list. Whenever a FIFO slot is freed up, the next frame (or A-MPDU) from the
pending queue gets moved to that slot.

This process is not only inefficient, but also unnecessary. The code can
be improved visibly by keeping the pending queue fully linked, and moving
the contents of the entire queue to a FIFO slot as it becomes available.

This patch makes the necessary changes for that and also merges some code
that was duplicated for EDMA vs non-EDMA. It changes txq->axq_link to point
to the last descriptor instead of the link pointer, so that
ath9k_hw_set_desc_link can be used, which works on all chips.

With this patch, a small performance increase for non-aggregated traffic
was observed on AR9380 based embedded hardware.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -179,7 +179,7 @@ enum ATH_AGGR_STATUS {
 struct ath_txq {
 	int mac80211_qnum; /* mac80211 queue number, -1 means not mac80211 Q */
 	u32 axq_qnum; /* ath9k hardware queue number */
-	u32 *axq_link;
+	void *axq_link;
 	struct list_head axq_q;
 	spinlock_t axq_lock;
 	u32 axq_depth;
@@ -188,7 +188,6 @@ struct ath_txq {
 	bool axq_tx_inprogress;
 	struct list_head axq_acq;
 	struct list_head txq_fifo[ATH_TXFIFO_DEPTH];
-	struct list_head txq_fifo_pending;
 	u8 txq_headidx;
 	u8 txq_tailidx;
 	int pending_frames;

drivers/net/wireless/ath/ath9k/debug.c

@@ -587,7 +587,6 @@ static ssize_t read_file_xmit(struct file *file, char __user *user_buf,
 
 	PRQLE("axq_q empty:       ", axq_q);
 	PRQLE("axq_acq empty:     ", axq_acq);
-	PRQLE("txq_fifo_pending:  ", txq_fifo_pending);
 	for (i = 0; i < ATH_TXFIFO_DEPTH; i++) {
 		snprintf(tmp, sizeof(tmp) - 1, "txq_fifo[%i] empty: ", i);
 		PRQLE(tmp, txq_fifo[i]);

drivers/net/wireless/ath/ath9k/main.c

@@ -62,8 +62,6 @@ static bool ath9k_has_pending_frames(struct ath_softc *sc, struct ath_txq *txq)
 
 	if (txq->axq_depth || !list_empty(&txq->axq_acq))
 		pending = true;
-	else if (sc->sc_ah->caps.hw_caps & ATH9K_HW_CAP_EDMA)
-		pending = !list_empty(&txq->txq_fifo_pending);
 
 	spin_unlock_bh(&txq->axq_lock);
 	return pending;