package/kernel/mac80211/patches/308-rt2x00-do-not-align-payload-on-modern-H-W.patch

   1 From: Stanislaw Gruszka <sgruszka@redhat.com>
   2 Date: Sun, 2 Nov 2014 13:38:47 +0100
   3 Subject: [PATCH] rt2x00: do not align payload on modern H/W
   4
   5 RT2800 and newer hardware require padding between header and payload if
   6 header length is not multiple of 4.
   7
   8 For historical reasons we also align payload to to 4 bytes boundary, but
   9 such alignment is not needed on modern H/W.
  10
  11 Patch improve performance on embedded CPUs and _possibly_ fixes
  12 skb_under_panic problems reported from time to time:
  13
  14 https://bugzilla.kernel.org/show_bug.cgi?id=84911
  15 https://bugzilla.kernel.org/show_bug.cgi?id=72471
  16 http://marc.info/?l=linux-wireless&m=139108549530402&w=2
  17 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1087591
  18
  19 But we can not explain or otherwise confirm the patch fixes this panic
  20 issue for sure.
  21
  22 Originally-From: Helmut Schaa <helmut.schaa@googlemail.com>
  23 Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
  24 ---
  25
  26 --- a/drivers/net/wireless/rt2x00/rt2x00queue.c
  27 +++ b/drivers/net/wireless/rt2x00/rt2x00queue.c
  28 @@ -158,55 +158,29 @@ void rt2x00queue_align_frame(struct sk_b
  29         skb_trim(skb, frame_length);
  30  }
  31
  32 -void rt2x00queue_insert_l2pad(struct sk_buff *skb, unsigned int header_length)
  33 +/*
  34 + * H/W needs L2 padding between the header and the paylod if header size
  35 + * is not 4 bytes aligned.
  36 + */
  37 +void rt2x00queue_insert_l2pad(struct sk_buff *skb, unsigned int hdr_len)
  38  {
  39 -       unsigned int payload_length = skb->len - header_length;
  40 -       unsigned int header_align = ALIGN_SIZE(skb, 0);
  41 -       unsigned int payload_align = ALIGN_SIZE(skb, header_length);
  42 -       unsigned int l2pad = payload_length ? L2PAD_SIZE(header_length) : 0;
  43 +       unsigned int l2pad = (skb->len > hdr_len) ? L2PAD_SIZE(hdr_len) : 0;
  44
  45 -       /*
  46 -        * Adjust the header alignment if the payload needs to be moved more
  47 -        * than the header.
  48 -        */
  49 -       if (payload_align > header_align)
  50 -               header_align += 4;
  51 -
  52 -       /* There is nothing to do if no alignment is needed */
  53 -       if (!header_align)
  54 +       if (!l2pad)
  55                 return;
  56
  57 -       /* Reserve the amount of space needed in front of the frame */
  58 -       skb_push(skb, header_align);
  59 -
  60 -       /*
  61 -        * Move the header.
  62 -        */
  63 -       memmove(skb->data, skb->data + header_align, header_length);
  64 -
  65 -       /* Move the payload, if present and if required */
  66 -       if (payload_length && payload_align)
  67 -               memmove(skb->data + header_length + l2pad,
  68 -                       skb->data + header_length + l2pad + payload_align,
  69 -                       payload_length);
  70 -
  71 -       /* Trim the skb to the correct size */
  72 -       skb_trim(skb, header_length + l2pad + payload_length);
  73 +       skb_push(skb, l2pad);
  74 +       memmove(skb->data, skb->data + l2pad, hdr_len);
  75  }
  76
  77 -void rt2x00queue_remove_l2pad(struct sk_buff *skb, unsigned int header_length)
  78 +void rt2x00queue_remove_l2pad(struct sk_buff *skb, unsigned int hdr_len)
  79  {
  80 -       /*
  81 -        * L2 padding is only present if the skb contains more than just the
  82 -        * IEEE 802.11 header.
  83 -        */
  84 -       unsigned int l2pad = (skb->len > header_length) ?
  85 -                               L2PAD_SIZE(header_length) : 0;
  86 +       unsigned int l2pad = (skb->len > hdr_len) ? L2PAD_SIZE(hdr_len) : 0;
  87
  88         if (!l2pad)
  89                 return;
  90
  91 -       memmove(skb->data + l2pad, skb->data, header_length);
  92 +       memmove(skb->data + l2pad, skb->data, hdr_len);
  93         skb_pull(skb, l2pad);
  94  }
  95