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

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Message-ID: <360914ee-594c-86bc-2436-aa863a67953a@microchip.com>
Date:   Tue, 5 Apr 2022 10:02:34 +0000
From:   <Codrin.Ciubotariu@...rochip.com>
To:     <michael@...le.cc>
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

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.

Best regards,
Codrin