rt2x00: Fix ieee80211 payload alignment

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>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 10 insertions, 3 deletions

diff --git a/drivers/net/wireless/rt2x00/rt2x00pci.c b/drivers/net/wireless/rt2x00/rt2x00pci.c
index 6d5d9aba0b..04663eb319 100644
--- a/drivers/net/wireless/rt2x00/rt2x00pci.c
+++ b/drivers/net/wireless/rt2x00/rt2x00pci.c
@@ -149,7 +149,7 @@ 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 ab4797ed94..568d73847d 100644
--- a/drivers/net/wireless/rt2x00/rt2x00usb.c
+++ b/drivers/net/wireless/rt2x00/rt2x00usb.c
@@ -245,13 +245,20 @@ 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);
 
         /*