[PATCH] rt2x00: Fix ieee80211 payload alignment

[PATCH] rt2x00: Fix ieee80211 payload alignment

[Ivo van Doorn]

As Johannes Berg indicated, the NET_IP_ALIGN doesn't
need to be used for ieee80211 frames. This means we
can simplify the alignment calculation to just
use the result of the header size modulus 4 as frame
alignment.

Furthermore we shouldn't use NET_IP_ALIGN in rt2x00usb
because it could be 0 on some architectures and we absolutely
need to have 2 bytes reserved for possible aligning.

Signed-off-by: Ivo van Doorn<IvDoorn@gmail.com>
---

John, please push this patch upstream to 2.6.24 as well.
This patch fixes a bug introduced in:
	rt2x00: Put 802.11 data on 4 byte boundary

 drivers/net/wireless/rt2x00/rt2x00pci.c |    2 +-
 drivers/net/wireless/rt2x00/rt2x00usb.c |   11 +++++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/rt2x00/rt2x00pci.c b/drivers/net/wireless/rt2x00/rt2x00pci.c
index 67e0779..ea15230 100644
--- a/drivers/net/wireless/rt2x00/rt2x00pci.c
+++ b/drivers/net/wireless/rt2x00/rt2x00pci.c
@@ -157,7 +157,7 @@ void rt2x00pci_rxdone(struct rt2x00_dev *rt2x00dev)
 		 * The data behind the ieee80211 header must be
 		 * aligned on a 4 byte boundary.
 		 */
-		align = NET_IP_ALIGN + (2 * (header_size % 4 == 0));
+		align = header_size % 4;
 
 		/*
 		 * Allocate the sk_buffer, initialize it and copy
diff --git a/drivers/net/wireless/rt2x00/rt2x00usb.c b/drivers/net/wireless/rt2x00/rt2x00usb.c
index 5e60504..f29a5dd 100644
--- a/drivers/net/wireless/rt2x00/rt2x00usb.c
+++ b/drivers/net/wireless/rt2x00/rt2x00usb.c
@@ -271,13 +271,20 @@ static void rt2x00usb_interrupt_rxdone(struct urb *urb)
 	 * Allocate a new sk buffer to replace the current one.
 	 * If allocation fails, we should drop the current frame
 	 * so we can recycle the existing sk buffer for the new frame.
+	 * As alignment we use 2 and not NET_IP_ALIGN because we need
+	 * to be sure we have 2 bytes room in the head. (NET_IP_ALIGN
+	 * can be 0 on some hardware). We use these 2 bytes for frame
+	 * alignment later, we assume that the chance that
+	 * header_size % 4 == 2 is bigger then header_size % 2 == 0
+	 * and thus optimize alignment by reserving the 2 bytes in
+	 * advance.
 	 */
 	frame_size = entry->ring->data_size + entry->ring->desc_size;
-	skb = dev_alloc_skb(frame_size + NET_IP_ALIGN);
+	skb = dev_alloc_skb(frame_size + 2);
 	if (!skb)
 		goto skip_entry;
 
-	skb_reserve(skb, NET_IP_ALIGN);
+	skb_reserve(skb, 2);
 	skb_put(skb, frame_size);
 
 	/*
-- 
1.5.3.8