Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 1/6] net: stmmac: use correct DMA buffer size in the RX
 descriptor
To:     Aaro Koskinen <aaro.koskinen@iki.fi>,
        "David S. Miller" <davem@davemloft.net>,
        Jose Abreu <jose.abreu@synopsys.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        <netdev@vger.kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        Aaro Koskinen <aaro.koskinen@nokia.com>
References: <20190327203540.1884-1-aaro.koskinen@iki.fi>
 <20190327203540.1884-2-aaro.koskinen@iki.fi>
From:   Jose Abreu <jose.abreu@synopsys.com>
Message-ID: <5c480a83-dfcf-c20c-f277-4449a7b41403@synopsys.com>
Date:   Fri, 29 Mar 2019 10:02:20 +0000
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.5.1
MIME-Version: 1.0
In-Reply-To: <20190327203540.1884-2-aaro.koskinen@iki.fi>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 3/27/2019 8:35 PM, Aaro Koskinen wrote:
> From: Aaro Koskinen <aaro.koskinen@nokia.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@nokia.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