ath5k: use rx hw descriptor pointer for self-linked check

This patch simplifies the code used to detect when the
self-linked DMA buffer is still in use by hardware, by
checking the hardware's rxdp register instead of looking
at the software buffer list.
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/base.c

@@ -1780,7 +1780,7 @@ ath5k_tasklet_rx(unsigned long data)
 	struct sk_buff *skb, *next_skb;
 	dma_addr_t next_skb_addr;
 	struct ath5k_softc *sc = (void *)data;
-	struct ath5k_buf *bf, *bf_last;
+	struct ath5k_buf *bf;
 	struct ath5k_desc *ds;
 	int ret;
 	int hdrlen;
@@ -1791,7 +1791,6 @@ ath5k_tasklet_rx(unsigned long data)
 		ATH5K_WARN(sc, "empty rx buf pool\n");
 		goto unlock;
 	}
-	bf_last = list_entry(sc->rxbuf.prev, struct ath5k_buf, list);
 	do {
 		rxs.flag = 0;
 
@@ -1800,24 +1799,9 @@ ath5k_tasklet_rx(unsigned long data)
 		skb = bf->skb;
 		ds = bf->desc;
 
-		/*
-		 * last buffer must not be freed to ensure proper hardware
-		 * function. When the hardware finishes also a packet next to
-		 * it, we are sure, it doesn't use it anymore and we can go on.
-		 */
-		if (bf_last == bf)
-			bf->flags |= 1;
-		if (bf->flags) {
-			struct ath5k_buf *bf_next = list_entry(bf->list.next,
-					struct ath5k_buf, list);
-			ret = sc->ah->ah_proc_rx_desc(sc->ah, bf_next->desc,
-					&rs);
-			if (ret)
+		/* bail if HW is still using self-linked descriptor */
+		if (ath5k_hw_get_rxdp(sc->ah) == bf->daddr)
 			break;
-			bf->flags &= ~1;
-			/* skip the overwritten one (even status is martian) */
-			goto next;
-		}
 
 		ret = sc->ah->ah_proc_rx_desc(sc->ah, ds, &rs);
 		if (unlikely(ret == -EINPROGRESS))

drivers/net/wireless/ath/ath5k/base.h

@@ -56,7 +56,6 @@
 
 struct ath5k_buf {
 	struct list_head	list;
-	unsigned int		flags;	/* rx descriptor flags */
 	struct ath5k_desc	*desc;	/* virtual addr of desc */
 	dma_addr_t		daddr;	/* physical addr of desc */
 	struct sk_buff		*skb;	/* skbuff for buf */

drivers/net/wireless/ath/ath5k/dma.c

@@ -80,8 +80,6 @@ int ath5k_hw_stop_rx_dma(struct ath5k_hw *ah)
  * ath5k_hw_get_rxdp - Get RX Descriptor's address
  *
  * @ah: The &struct ath5k_hw
- *
- * XXX: Is RXDP read and clear ?
  */
 u32 ath5k_hw_get_rxdp(struct ath5k_hw *ah)
 {