netdev - Re: [PATCH net v3] ravb: do not use zero-length alignment DMA descriptor

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Message-Id: <20170116.115350.943642905478824707.davem@davemloft.net>
Date:   Mon, 16 Jan 2017 11:53:50 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sergei.shtylyov@...entembedded.com
Cc:     horms+renesas@...ge.net.au, magnus.damm@...il.com,
        netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        masaru.nagai.vx@...esas.com
Subject: Re: [PATCH net v3] ravb: do not use zero-length alignment DMA
 descriptor

From: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Date: Mon, 16 Jan 2017 16:01:49 +0300

> On 01/16/2017 01:45 PM, Simon Horman wrote:
> 
>> From: Masaru Nagai <masaru.nagai.vx@...esas.com>
>>
>> Due to alignment requirements of the hardware transmissions are split
>> into
>> two DMA descriptors, a small padding descriptor of 0 - 3 bytes in
>> length
>> followed by a descriptor for rest of the packet.
>>
>> In the case of IP packets the first descriptor will never be zero due
>> to
>> the way that the stack aligns buffers for IP packets. However, for
>> non-IP
>> packets it may be zero.
>>
>> In that case it has been reported that timeouts occur, presumably
>> because
>> transmission stops at the first zero-length DMA descriptor and thus
>> the
>> packet is not transmitted. However, in my environment a BUG is
>> triggered as
>> follows:
> [...]
> 
>> Fixes: 2f45d1902acf ("ravb: minimize TX data copying")
>> Signed-off-by: Masaru Nagai <masaru.nagai.vx@...esas.com
>> Signed-off-by: Simon Horman <horms+renesas@...ge.net.au>
> 
> Acked-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>

Applied and queued up for -stable, thanks.