[wireless-next][PATCH 2/3] b43: use 8K buffers for 64-bit DMA to workaround hardware bug

[Rafał Miłecki]

Signed-off-by: Rafał Miłecki <zaj...@gmail.com>
---
 drivers/net/wireless/b43/dma.c |   24 ++++++++++++++++--------
 drivers/net/wireless/b43/dma.h |    3 ++-
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireless/b43/dma.c b/drivers/net/wireless/b43/dma.c
index e36e8b5..5e45604 100644
--- a/drivers/net/wireless/b43/dma.c
+++ b/drivers/net/wireless/b43/dma.c
@@ -419,26 +419,34 @@ static int alloc_ringmemory(struct b43_dmaring *ring)
        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);
 }
 
diff --git a/drivers/net/wireless/b43/dma.h b/drivers/net/wireless/b43/dma.h
index 7e20b04..315b96e 100644
--- a/drivers/net/wireless/b43/dma.h
+++ b/drivers/net/wireless/b43/dma.h
@@ -161,7 +161,8 @@ struct b43_dmadesc_generic {
 } __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
-- 
1.7.1


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