[PATCH 3.12 48/88] net: alx: Work around the DMA RX overflow issue

From: Jiri Slaby
Date: Thu Jul 14 2016 - 04:30:43 EST

From: Feng Tang <feng.tang@xxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


[ Upstream commit 881d0327db37ad917a367c77aff1afa1ee41e0a9 ]

Note: This is a verified backported patch for stable 4.4 kernel, and it
could also be applied to 4.3/4.2/4.1/3.18/3.16

There is a problem with alx devices, that the network link will be
lost in 1-5 minutes after the device is up.

>From debugging without datasheet, we found the error always
happen when the DMA RX address is set to 0x....fc0, which is very
likely to be a HW/silicon problem.

This patch will apply rx skb with 64 bytes longer space, and if the
allocated skb has a 0x...fc0 address, it will use skb_resever(skb, 64)
to advance the address, so that the RX overflow can be avoided.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=70761
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Tested-by: Ole Lukoie <olelukoie@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
drivers/net/ethernet/atheros/alx/main.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/atheros/alx/main.c b/drivers/net/ethernet/atheros/alx/main.c
index 754ac8ef2484..4736df41f062 100644
--- a/drivers/net/ethernet/atheros/alx/main.c
+++ b/drivers/net/ethernet/atheros/alx/main.c
@@ -86,9 +86,14 @@ static int alx_refill_rx_ring(struct alx_priv *alx, gfp_t gfp)
while (!cur_buf->skb && next != rxq->read_idx) {
struct alx_rfd *rfd = &rxq->rfd[cur];

- skb = __netdev_alloc_skb(alx->dev, alx->rxbuf_size, gfp);
+ skb = __netdev_alloc_skb(alx->dev, alx->rxbuf_size + 64, gfp);
if (!skb)
+ /* Workround for the HW RX DMA overflow issue */
+ if (((unsigned long)skb->data & 0xfff) == 0xfc0)
+ skb_reserve(skb, 64);
dma = dma_map_single(&alx->hw.pdev->dev,
skb->data, alx->rxbuf_size,