linux-kernel - Re: [PATCH] i2c: at91: use dma safe buffers

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Date:   Tue, 05 Apr 2022 11:38:48 +0200
From:   Michael Walle <michael@...le.cc>
To:     Codrin.Ciubotariu@...rochip.com
Cc:     Nicolas.Ferre@...rochip.com, alexandre.belloni@...tlin.com,
        Claudiu.Beznea@...rochip.com, sumit.semwal@...aro.org,
        christian.koenig@....com, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, stable@...r.kernel.org
Subject: Re: [PATCH] i2c: at91: use dma safe buffers

Am 2022-04-05 11:23, schrieb Codrin.Ciubotariu@...rochip.com:
> On 03.03.2022 18:17, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
>> the content is safe
>> 
>> The supplied buffer might be on the stack and we get the following 
>> error
>> message:
>> [    3.312058] at91_i2c e0070600.i2c: rejecting DMA map of vmalloc 
>> memory
>> 
>> Use i2c_{get,put}_dma_safe_msg_buf() to get a DMA-able memory region 
>> if
>> necessary.
>> 
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Michael Walle <michael@...le.cc>
> 
> Reviewed-by: Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>

Thanks!

>> I'm not sure if or which Fixes: tag I should add to this patch. The 
>> issue
>> seems to be since a very long time, but nobody seem to have triggered 
>> it.
>> FWIW, I'm using the sff,sfp driver, which triggers this.
> 
> I think it should be:
> Fixes: 60937b2cdbf9 ("i2c: at91: add dma support")
> 
>> +       if (dev->use_dma) {
>> +               dma_buf = i2c_get_dma_safe_msg_buf(m_start, 1);
> 
> If you want, you could just dev->buf = i2c_get_dma_safe...

But where is the error handling in that case? dev->buf will
be NULL, which is eventually passed to dma_map_single().

Also, I need the dma_buf for the i2c_put_dma_safe_msg_buf()
call anyway, because dev->buf will be modified during
processing.

-michael