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

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Message-ID: <96396803-caac-13cd-3e17-f9d10fc608ad@cogentembedded.com>
Date:   Mon, 16 Jan 2017 16:01:49 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Simon Horman <horms+renesas@...ge.net.au>,
        David Miller <davem@...emloft.net>
Cc:     Magnus Damm <magnus.damm@...il.com>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Masaru Nagai <masaru.nagai.vx@...esas.com>
Subject: Re: [PATCH net v3] ravb: do not use zero-length alignment DMA
 descriptor

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>

MBR, Sergei