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>
diff --git a/drivers/net/wireless/iwlwifi/iwl-agn.c b/drivers/net/wireless/iwlwifi/iwl-agn.c
index 6751bb2..444c5cc 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn.c
@@ -1384,7 +1384,7 @@
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 @@
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);