rtlwifi: usb: add NET_IP_ALIGN padding to RX skb when needed

Add proper alignment at first packet copy, to avoid extra copies made later
in networking stack.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/drivers/net/wireless/rtlwifi/usb.c b/drivers/net/wireless/rtlwifi/usb.c
index a7b54f6..72c2614 100644 (file)
--- a/drivers/net/wireless/rtlwifi/usb.c
+++ b/drivers/net/wireless/rtlwifi/usb.c
@@ -569,6 +569,37 @@ static void _rtl_rx_work(unsigned long param)
        }
 }
 
+static unsigned int _rtl_rx_get_padding(struct ieee80211_hdr *hdr,
+                                       unsigned int len)
+{
+       unsigned int padding = 0;
+
+       /* make function no-op when possible */
+       if (NET_IP_ALIGN == 0 || len < sizeof(*hdr))
+               return 0;
+
+       /* alignment calculation as in lbtf_rx() / carl9170_rx_copy_data() */
+       /* TODO: deduplicate common code, define helper function instead? */
+
+       if (ieee80211_is_data_qos(hdr->frame_control)) {
+               u8 *qc = ieee80211_get_qos_ctl(hdr);
+
+               padding ^= NET_IP_ALIGN;
+
+               /* Input might be invalid, avoid accessing memory outside
+                * the buffer.
+                */
+               if ((unsigned long)qc - (unsigned long)hdr < len &&
+                   *qc & IEEE80211_QOS_CTL_A_MSDU_PRESENT)
+                       padding ^= NET_IP_ALIGN;
+       }
+
+       if (ieee80211_has_a4(hdr->frame_control))
+               padding ^= NET_IP_ALIGN;
+
+       return padding;
+}
+
 #define __RADIO_TAP_SIZE_RSV   32
 
 static void _rtl_rx_completed(struct urb *_urb)
@@ -582,9 +613,11 @@ static void _rtl_rx_completed(struct urb *_urb)
                goto free;
 
        if (likely(0 == _urb->status)) {
+               unsigned int padding;
                struct sk_buff *skb;
                unsigned int qlen;
                unsigned int size = _urb->actual_length;
+               struct ieee80211_hdr *hdr;
 
                if (size < RTL_RX_DESC_SIZE + sizeof(struct ieee80211_hdr)) {
                        RT_TRACE(rtlpriv, COMP_USB, DBG_EMERG,
@@ -601,7 +634,10 @@ static void _rtl_rx_completed(struct urb *_urb)
                        goto resubmit;
                }
 
-               skb = dev_alloc_skb(size + __RADIO_TAP_SIZE_RSV);
+               hdr = (void *)(_urb->transfer_buffer + RTL_RX_DESC_SIZE);
+               padding = _rtl_rx_get_padding(hdr, size - RTL_RX_DESC_SIZE);
+
+               skb = dev_alloc_skb(size + __RADIO_TAP_SIZE_RSV + padding);
                if (!skb) {
                        RT_TRACE(rtlpriv, COMP_USB, DBG_EMERG,
                                 "Can't allocate skb for bulk IN!\n");
@@ -610,6 +646,9 @@ static void _rtl_rx_completed(struct urb *_urb)
 
                _rtl_install_trx_info(rtlusb, skb, rtlusb->in_ep);
 
+               /* Make sure the payload data is 4 byte aligned. */
+               skb_reserve(skb, padding);
+
                /* reserve some space for mac80211's radiotap */
                skb_reserve(skb, __RADIO_TAP_SIZE_RSV);