B43: Handle DMA RX descriptor underrun

Add handling of rx descriptor underflow. This fixes a fault that could
happen on slow machines, where data is received faster than the CPU can
handle. In such a case the device will use up all rx descriptors and
refuse to send any more data before confirming that it is ok. This
patch enables necessary interrupt to discover such a situation and will
handle them by dropping everything in the ring buffer.

Reviewed-by: Michael Buesch <m@bues.ch>
Signed-off-by: Thommy Jakobsson <thommyj@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43/dma.h b/drivers/net/wireless/b43/dma.h
index 9fdd198..df8c8cd 100644
--- a/drivers/net/wireless/b43/dma.h
+++ b/drivers/net/wireless/b43/dma.h
@@ -9,7 +9,7 @@
 /* DMA-Interrupt reasons. */
 #define B43_DMAIRQ_FATALMASK	((1 << 10) | (1 << 11) | (1 << 12) \
 					 | (1 << 14) | (1 << 15))
-#define B43_DMAIRQ_NONFATALMASK	(1 << 13)
+#define B43_DMAIRQ_RDESC_UFLOW		(1 << 13)
 #define B43_DMAIRQ_RX_DONE		(1 << 16)
 
 /*** 32-bit DMA Engine. ***/
@@ -295,6 +295,8 @@
 void b43_dma_handle_txstatus(struct b43_wldev *dev,
 			     const struct b43_txstatus *status);
 
+void b43_dma_handle_rx_overflow(struct b43_dmaring *ring);
+
 void b43_dma_rx(struct b43_dmaring *ring);
 
 void b43_dma_direct_fifo_rx(struct b43_wldev *dev,