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SubjectRe: [PATCH v2] marvell sky2 driver: fix so it works without unaligned accesses
On Wed, 4 Apr 2012 10:13:32 -0400
Chris Metcalf <cmetcalf@tilera.com> wrote:

> The driver uses a receive_new() routine that ends up requiring unaligned
> accesses in IP header processing. If the architecture doesn't support
> efficient unaligned accesses, and SKY2_HW_RAM_BUFFER is set,
> just copy all ingress packets to the bounce buffers instead.
> Thanks to Eric Dumazet for pointing out the SKY2_HW_RAM_BUFFER issue.
>
> This allows the driver to be used on the Tilera TILEmpower-Gx, since
> the tile architecture doesn't currently handle kernel unaligned accesses,
> just userspace.
>
> Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
> ---
> drivers/net/ethernet/marvell/sky2.c | 6 +++++-
> 1 files changed, 5 insertions(+), 1 deletions(-)

What about the following (compile tested only)
--- a/drivers/net/ethernet/marvell/sky2.c 2012-04-04 08:49:05.954853108 -0700
+++ b/drivers/net/ethernet/marvell/sky2.c 2012-04-04 11:30:54.201432707 -0700
@@ -2468,6 +2468,17 @@ static int sky2_change_mtu(struct net_de
return err;
}

+static inline bool needs_copy(const struct rx_ring_info *re,
+ unsigned length)
+{
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+ /* Some architectures need the IP header to be aligned */
+ if (!IS_ALIGNED(re->data_addr + ETH_HLEN, sizeof(u32)))
+ return 1;
+#endif
+ return length < copybreak;
+}
+
/* For small just reuse existing skb for next receive */
static struct sk_buff *receive_copy(struct sky2_port *sky2,
const struct rx_ring_info *re,
@@ -2605,7 +2616,7 @@ static struct sk_buff *sky2_receive(stru
goto error;

okay:
- if (length < copybreak)
+ if (needs_copy(re, length))
skb = receive_copy(sky2, re, length);
else
skb = receive_new(sky2, re, length);

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