b43: use 8K buffers for 64-bit DMA to workaround hardware bug

Signed-off-by: Rafał Miłecki <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

drivers/net/wireless/b43/dma.c

···
 	gfp_t flags = GFP_KERNEL;
 
 	/* The specs call for 4K buffers for 30- and 32-bit DMA with 4K
-	 * alignment and 8K buffers for 64-bit DMA with 8K alignment. Testing
-	 * has shown that 4K is sufficient for the latter as long as the buffer
-	 * does not cross an 8K boundary.
-	 *
+	 * alignment and 8K buffers for 64-bit DMA with 8K alignment.
+	 * In practice we could use smaller buffers for the latter, but the
+	 * alignment is really important because of the hardware bug. If bit
+	 * 0x00001000 is used in DMA address, some hardware (like BCM4331)
+	 * copies that bit into B43_DMA64_RXSTATUS and we get false values from
+	 * B43_DMA64_RXSTATDPTR. Let's just use 8K buffers even if we don't use
+	 * more than 256 slots for ring.
 	 */
+	u16 ring_mem_size = (ring->type == B43_DMA_64BIT) ?
+				B43_DMA64_RINGMEMSIZE : B43_DMA32_RINGMEMSIZE;
+
 	ring->descbase = dma_alloc_coherent(ring->dev->dev->dma_dev,
-					    B43_DMA_RINGMEMSIZE,
-					    &(ring->dmabase), flags);
+					    ring_mem_size, &(ring->dmabase),
+					    flags);
 	if (!ring->descbase) {
 		b43err(ring->dev->wl, "DMA ringmemory allocation failed\n");
 		return -ENOMEM;
 	}
-	memset(ring->descbase, 0, B43_DMA_RINGMEMSIZE);
+	memset(ring->descbase, 0, ring_mem_size);
 
 	return 0;
 }
 
 static void free_ringmemory(struct b43_dmaring *ring)
 {
-	dma_free_coherent(ring->dev->dev->dma_dev, B43_DMA_RINGMEMSIZE,
+	u16 ring_mem_size = (ring->type == B43_DMA_64BIT) ?
+				B43_DMA64_RINGMEMSIZE : B43_DMA32_RINGMEMSIZE;
+	dma_free_coherent(ring->dev->dev->dma_dev, ring_mem_size,
 			  ring->descbase, ring->dmabase);
 }
 

drivers/net/wireless/b43/dma.h

···
 } __packed;
 
 /* Misc DMA constants */
-#define B43_DMA_RINGMEMSIZE		PAGE_SIZE
+#define B43_DMA32_RINGMEMSIZE		4096
+#define B43_DMA64_RINGMEMSIZE		8192
 /* Offset of frame with actual data */
 #define B43_DMA0_RX_FW598_FO		38
 #define B43_DMA0_RX_FW351_FO		30