linux-kernel - Re: [PATCH v2] iio: adc: stm32-adc: Use dma_request_chan() instead dma_request_slave

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Date:   Wed, 8 Jan 2020 10:04:14 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Fabrice Gasnier <fabrice.gasnier@...com>, <jic23@...nel.org>,
        <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>
CC:     <vkoul@...nel.org>, <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        Olivier MOYSAN <olivier.moysan@...com>
Subject: Re: [PATCH v2] iio: adc: stm32-adc: Use dma_request_chan() instead
 dma_request_slave_channel()

Hi Fabrice,

On 07/01/2020 19.15, Fabrice Gasnier wrote:
> On 1/7/20 12:41 PM, Peter Ujfalusi wrote:
>> dma_request_slave_channel() is a wrapper on top of dma_request_chan()
>> eating up the error code.
>>
>> By using dma_request_chan() directly the driver can support deferred
>> probing against DMA.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
>> ---
>> Hi,
>>
>> Changes since v1:
>> - Fall back to IRQ mode only in case of ENODEV
>>
>> Regards,
>> Peter
> 
> Hi Peter,
> 
> Thanks for the patch,
> 
> In case you send another version... I've just a minor suggestion
> regarding the comment (see after). Apart from that, you can add my:

Thanks, I'll take your suggested update and send v3.

> Acked-by: Fabrice Gasnier <fabrice.gasnier@...com>
> 
> Best Regards,
> Fabrice
> 
>>
>>  drivers/iio/adc/stm32-adc.c | 16 ++++++++++++++--
>>  1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
>> index 3b291d72701c..df5f5d61f9f9 100644
>> --- a/drivers/iio/adc/stm32-adc.c
>> +++ b/drivers/iio/adc/stm32-adc.c
>> @@ -1746,9 +1746,21 @@ static int stm32_adc_dma_request(struct iio_dev *indio_dev)
>>  	struct dma_slave_config config;
>>  	int ret;
>>  
>> -	adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
>> -	if (!adc->dma_chan)
>> +	adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx");
>> +	if (IS_ERR(adc->dma_chan)) {
>> +		ret = PTR_ERR(adc->dma_chan);
>> +		if (ret != -ENODEV) {
>> +			if (ret != -EPROBE_DEFER)
>> +				dev_err(&indio_dev->dev,
>> +					"DMA channel request failed with %d\n",
>> +					ret);
>> +			return ret;
>> +		}
>> +
>> +		/* Ignore errors to fall back to IRQ mode */
> 		               ^
> 		          error
> alternate suggestion:
> 		/* DMA is optional: fall back to IRQ mode */

Makes more sense in the context.

> 
>> +		adc->dma_chan = NULL;
>>  		return 0;
>> +	}
>>  
>>  	adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
>>  					 STM32_DMA_BUFFER_SIZE,
>>

- Péter

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