ath: add common ath_rxbuf_alloc() and make ath9k use it

Turns out ath5k and ath9k can share the same helper to
allocates RX skbs. We allocate skbs aligned to the cache line
size. This requirement seems to have come from AR5210; when
this was not done it seems sometimes we'd get bogus data. I'm
also told it may have been a performance enhancement
consideration. In the end I can't be sure we can remove this
on new hardware so just keep this and start sharing it through
ath.ko.

Make ath9k start using this, ath5k is next.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/net/wireless/ath/main.c b/drivers/net/wireless/ath/main.c
index 9949b11cb151..487193f1de1a 100644
--- a/drivers/net/wireless/ath/main.c
+++ b/drivers/net/wireless/ath/main.c
@@ -17,6 +17,42 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 
+#include "ath.h"
+
 MODULE_AUTHOR("Atheros Communications");
 MODULE_DESCRIPTION("Shared library for Atheros wireless LAN cards.");
 MODULE_LICENSE("Dual BSD/GPL");
+
+struct sk_buff *ath_rxbuf_alloc(struct ath_common *common,
+                                u32 len,
+                                gfp_t gfp_mask)
+{
+        struct sk_buff *skb;
+        u32 off;
+
+        /*
+         * Cache-line-align.  This is important (for the
+         * 5210 at least) as not doing so causes bogus data
+         * in rx'd frames.
+         */
+
+        /* Note: the kernel can allocate a value greater than
+         * what we ask it to give us. We really only need 4 KB as that
+         * is this hardware supports and in fact we need at least 3849
+         * as that is the MAX AMSDU size this hardware supports.
+         * Unfortunately this means we may get 8 KB here from the
+         * kernel... and that is actually what is observed on some
+         * systems :( */
+        skb = __dev_alloc_skb(len + common->cachelsz - 1, gfp_mask);
+        if (skb != NULL) {
+                off = ((unsigned long) skb->data) % common->cachelsz;
+                if (off != 0)
+                        skb_reserve(skb, common->cachelsz - off);
+        } else {
+                printk(KERN_ERR "skbuff alloc of size %u failed\n", len);
+                return NULL;
+        }
+
+        return skb;
+}
+EXPORT_SYMBOL(ath_rxbuf_alloc);