[PATCH 1/1] gianfar: fix a flooded alignment reports because of padding issue.

[Zumeng Chen]

According to LS1021A RM, the value of PAL can be set so that the start of the
IP header in the receive data buffer is aligned to a 32-bit boundary. Normally,
setting PAL = 2 provides minimal padding to ensure such alignment of the IP
header.

However every incoming packet's 8-byte time stamp will be inserted into the
packet data buffer as padding alignment bytes when hardware time stamping is
enabled.

So we set the padding 8+2 here to avoid the flooded alignment faults:

root@128:~# cat /proc/cpu/alignment
User:           0
System:         17539 (inet_gro_receive+0x114/0x2c0)
Skipped:        0
Half:           0
Word:           0
DWord:          0
Multi:          17539
User faults:    2 (fixup)

Also shown when exception report enablement

CPU: 0 PID: 161 Comm: irq/66-eth1_g0_ Not tainted 4.1.21-rt13-WR8.0.0.0_preempt-rt #16
Hardware name: Freescale LS1021A
[<8001b420>] (unwind_backtrace) from [<8001476c>] (show_stack+0x20/0x24)
[<8001476c>] (show_stack) from [<807cfb48>] (dump_stack+0x94/0xac)
[<807cfb48>] (dump_stack) from [<80025d70>] (do_alignment+0x720/0x958)
[<80025d70>] (do_alignment) from [<80009224>] (do_DataAbort+0x40/0xbc)
[<80009224>] (do_DataAbort) from [<80015398>] (__dabt_svc+0x38/0x60)
Exception stack(0x86ad1cc0 to 0x86ad1d08)
1cc0: f9b3e080 86b3d072 2d78d287 00000000 866816c0 86b3d05e 86e785d0 00000000
1ce0: 00000011 0000000e 80840ab0 86ad1d3c 86ad1d08 86ad1d08 806d7fc0 806d806c
1d00: 40070013 ffffffff
[<80015398>] (__dabt_svc) from [<806d806c>] (inet_gro_receive+0x114/0x2c0)
[<806d806c>] (inet_gro_receive) from [<80660eec>] (dev_gro_receive+0x21c/0x3c0)
[<80660eec>] (dev_gro_receive) from [<8066133c>] (napi_gro_receive+0x44/0x17c)
[<8066133c>] (napi_gro_receive) from [<804f0538>] (gfar_clean_rx_ring+0x39c/0x7d4)
[<804f0538>] (gfar_clean_rx_ring) from [<804f0bf4>] (gfar_poll_rx_sq+0x58/0xe0)
[<804f0bf4>] (gfar_poll_rx_sq) from [<80660b10>] (net_rx_action+0x27c/0x43c)
[<80660b10>] (net_rx_action) from [<80033638>] (do_current_softirqs+0x1e0/0x3dc)
[<80033638>] (do_current_softirqs) from [<800338c4>] (__local_bh_enable+0x90/0xa8)
[<800338c4>] (__local_bh_enable) from [<8008025c>] (irq_forced_thread_fn+0x70/0x84)
[<8008025c>] (irq_forced_thread_fn) from [<800805e8>] (irq_thread+0x16c/0x244)
[<800805e8>] (irq_thread) from [<8004e490>] (kthread+0xe8/0x104)
[<8004e490>] (kthread) from [<8000fda8>] (ret_from_fork+0x14/0x2c)

Signed-off-by: Zumeng Chen <zumeng.chen@xxxxxxxxx>
---

Hi,

This patch has been seen in arm and validated, and compile, boot, and ptpd testing passed in powerpc as well.
Not sure if it's the similar fix as fec_main.c did, all yours.

Cheers,

 drivers/net/ethernet/freescale/gianfar.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index e616b71..e47945f 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -1413,9 +1413,11 @@ static int gfar_probe(struct platform_device *ofdev)
 
 	gfar_init_addr_hash_table(priv);
 
-	/* Insert receive time stamps into padding alignment bytes */
+	/* Insert receive time stamps into padding alignment bytes, and
+	 * plus 2 bytes padding to ensure the cpu alignment.
+	 */
 	if (priv->device_flags & FSL_GIANFAR_DEV_HAS_TIMER)
-		priv->padding = 8;
+		priv->padding = 8 + DEFAULT_PADDING;
 
 	if (dev->features & NETIF_F_IP_CSUM ||
 	    priv->device_flags & FSL_GIANFAR_DEV_HAS_TIMER)
-- 
2.5.0