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Date:   Tue, 05 Apr 2022 13:09:04 +0200
From:   Michael Walle <michael@walle.cc>
To:     Codrin.Ciubotariu@microchip.com
Cc:     Nicolas.Ferre@microchip.com, alexandre.belloni@bootlin.com,
        Claudiu.Beznea@microchip.com, sumit.semwal@linaro.org,
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Subject: Re: [PATCH] i2c: at91: use dma safe buffers
In-Reply-To: <360914ee-594c-86bc-2436-aa863a67953a@microchip.com>
References: <20220303161724.3324948-1-michael@walle.cc>
 <46e1be55-9377-75b7-634d-9eadbebc98d7@microchip.com>
 <bc32f1107786ebcbfb4952e1a6142304@walle.cc>
 <360914ee-594c-86bc-2436-aa863a67953a@microchip.com>
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Am 2022-04-05 12:02, schrieb Codrin.Ciubotariu@microchip.com:
> On 05.04.2022 12:38, Michael Walle wrote:
>> Am 2022-04-05 11:23, schrieb Codrin.Ciubotariu@microchip.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