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

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Date:   Tue, 05 Dec 2017 11:48:46 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     zumeng.chen@...il.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        claudiu.manoil@....com
Subject: Re: [PATCH 1/1] gianfar: fix a flooded alignment reports because
 of padding issue.

From: Zumeng Chen <zumeng.chen@...il.com>
Date: Mon, 4 Dec 2017 11:22:02 +0800

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

Applied.