linux-kernel - Re: [PATCH 1/6] net: stmmac: use correct DMA buffer size in the RX descriptor

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Date:   Fri, 29 Mar 2019 10:02:20 +0000
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     Aaro Koskinen <aaro.koskinen@....fi>,
        "David S. Miller" <davem@...emloft.net>,
        Jose Abreu <jose.abreu@...opsys.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        <netdev@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>,
        Aaro Koskinen <aaro.koskinen@...ia.com>
Subject: Re: [PATCH 1/6] net: stmmac: use correct DMA buffer size in the RX
 descriptor

On 3/27/2019 8:35 PM, Aaro Koskinen wrote:
> From: Aaro Koskinen <aaro.koskinen@...ia.com>
> 
> We always program the maximum DMA buffer size into the receive descriptor,
> although the allocated size may be less. E.g. with the default MTU size
> we allocate only 1536 bytes. If somebody sends us a bigger frame, then
> memory may get corrupted.
> 
> Fix by using exact buffer sizes.
> 
> Signed-off-by: Aaro Koskinen <aaro.koskinen@...ia.com>

So, I'm seeing that the maximum allowed buffer size that can be
put in the descriptor changes between enhanced descriptors to
normal descriptors (8KB vs. 2KB right ?).

Shouldn't stmmac_main know about this limit before trying to init
descriptors ?

We do limit the MTU according to HW version but I would rather
prefer not having to need to calculate min() values in the
descriptor code and just use the value as is ...

Thanks,
Jose Miguel Abreu