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

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Message-ID: <27f124c9adaf8a4fbdfb7a38456c4a2e@walle.cc>
Date:   Tue, 05 Apr 2022 13:09:04 +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 12:02, schrieb Codrin.Ciubotariu@...rochip.com:
> On 05.04.2022 12:38, Michael Walle wrote:
>> Am 2022-04-05 11:23, schrieb Codrin.Ciubotariu@...rochip.com:
>>>> +       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.
> 
> You still:
> 	if (!dev->buf) {
> 		ret = -ENOMEM;
> 		goto out;
> 	}
> 
> So, at91_do_twi_transfer()/dma_map_single() will not be called.

Ahh, I misunderstood you. Yes, but as I said, I need the dma_buf
temporary variable anyway, because dev->buf is modified, eg. see
at91_twi_read_data_dma_callback().

-michael