ath5k: Reset Tx interrupt bits also on PISR

Some cards don't update the PISR properly when all SISR bits
for Tx interrupts are being cleared and as a result we get
interrupt storm. Since we handle all tx queues all together
(so we don't really use the SISR bits to do per-queue interrupt
handling), we can manualy update PISR by doing a write-to-clear
on its Tx interrupt bits.
Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -616,7 +616,16 @@ ath5k_hw_get_isr(struct ath5k_hw *ah, enum ath5k_int *interrupt_mask)
 		 * SISRs will also clear PISR so no need to worry here.
 		 */
 
-		pisr_clear = pisr & ~AR5K_ISR_BITS_FROM_SISRS;
+		/* XXX: There seems to be  an issue on some cards
+		 *	with tx interrupt flags not being updated
+		 *	on PISR despite that all Tx interrupt bits
+		 * 	are cleared on SISRs. Since we handle all
+		 *	Tx queues all together it shouldn't be an
+		 *	issue if we clear Tx interrupt flags also
+		 * 	on PISR to avoid that.
+		 */
+		pisr_clear = (pisr & ~AR5K_ISR_BITS_FROM_SISRS) |
+					(pisr & AR5K_INT_TX_ALL);
 
 		/*
 		 * Write to clear them...