iwlagn: fix RX skb alignment

So I dug deeper into the DMA problems I had with iwlagn and a kind soul
helped me in that he said something about pci-e alignment and mentioned
the iwl_rx_allocate function to check for crossing 4KB boundaries. Since
there's 8KB A-MPDU support, crossing 4k boundaries didn't seem like
something the device would fail with, but when I looked into the
function for a minute anyway I stumbled over this little gem:

	BUG_ON(rxb->dma_addr & (~DMA_BIT_MASK(36) & 0xff));

Clearly, that is a totally bogus check, one would hope the compiler
removes it entirely. (Think about it)

After fixing it, I obviously ran into it, nothing guarantees the
alignment the way you want it,  because of the way skbs and their
headroom are allocated. I won't explain that here nor double-check that
I'm right, that goes beyond what most of the CC'ed people care about.

So then I came up with the patch below, and so far my system has
survived minutes with 64K pages, when it would previously fail in
seconds. And I haven't seen a single instance of the TX bug either. But
when you see the patch it'll be pretty obvious to you why.

This should fix the following reported kernel bugs:

http://bugzilla.kernel.org/show_bug.cgi?id=11596
http://bugzilla.kernel.org/show_bug.cgi?id=11393
http://bugzilla.kernel.org/show_bug.cgi?id=11983

I haven't checked if there are any elsewhere, but I suppose RHBZ will
have a few instances too...

I'd like to ask anyone who is CC'ed (those are people I know ran into
the bug) to try this patch.

I am convinced that this patch is correct in spirit, but I haven't
understood why, for example, there are so many unmap calls. I'm not
entirely convinced that this is the only bug leading to the TX reply
errors.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-agn.c b/drivers/net/wireless/iwlwifi/iwl-agn.c
index 6751bb2b8ae..444c5cc05f0 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn.c
@@ -1384,7 +1384,7 @@ void iwl_rx_handle(struct iwl_priv *priv)
 
 		rxq->queue[i] = NULL;
 
-		pci_dma_sync_single_for_cpu(priv->pci_dev, rxb->dma_addr,
+		pci_dma_sync_single_for_cpu(priv->pci_dev, rxb->aligned_dma_addr,
 					    priv->hw_params.rx_buf_size,
 					    PCI_DMA_FROMDEVICE);
 		pkt = (struct iwl_rx_packet *)rxb->skb->data;
@@ -1436,8 +1436,8 @@ void iwl_rx_handle(struct iwl_priv *priv)
 			rxb->skb = NULL;
 		}
 
-		pci_unmap_single(priv->pci_dev, rxb->dma_addr,
-				 priv->hw_params.rx_buf_size,
+		pci_unmap_single(priv->pci_dev, rxb->real_dma_addr,
+				 priv->hw_params.rx_buf_size + 256,
 				 PCI_DMA_FROMDEVICE);
 		spin_lock_irqsave(&rxq->lock, flags);
 		list_add_tail(&rxb->list, &priv->rxq.rx_used);