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

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Date:   Thu, 9 Jan 2020 12:32:02 +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-dfsdm: Use dma_request_chan() instead
 dma_request_slave_channel()



On 09/01/2020 11.13, Fabrice Gasnier wrote:
> On 1/7/20 12:45 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 for ADC only in case of ENODEV
> 
> Hi Peter,
> 
> Thanks for the patch,
> 
> Please find a minor comment here after. Apart from that, you can add my:
> 
> Acked-by: Fabrice Gasnier <fabrice.gasnier@...com>
> 
> 
>>
>> Regards,
>> Peter
>>
>>  drivers/iio/adc/stm32-dfsdm-adc.c | 21 +++++++++++++++++----
>>  1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
>> index e493242c266e..74a2211bdff4 100644
>> --- a/drivers/iio/adc/stm32-dfsdm-adc.c
>> +++ b/drivers/iio/adc/stm32-dfsdm-adc.c
>> @@ -1383,9 +1383,13 @@ static int stm32_dfsdm_dma_request(struct iio_dev *indio_dev)
>>  {
>>  	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
>>  
>> -	adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
>> -	if (!adc->dma_chan)
>> -		return -EINVAL;
>> +	adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx");
>> +	if (IS_ERR(adc->dma_chan)) {
>> +		int ret = PTR_ERR(adc->dma_chan);
>> +
>> +		adc->dma_chan = NULL;
>> +		return ret;
> 
> You may "return PTR_ERR(adc->dma_chan);" directly here.

I don't make decision here on behalf of the adc path on to go forward w/
or w/o DMA support and if we go ahead the stm32_dfsdm_dma_release()
needs the dma_chan to be NULL in case we don't use DMA.

It is much cleaner to set dma_chan to NULL here than doing it in other
paths.

> 
> Best Regards,
> Fabrice
> 
>> +	}
>>  
>>  	adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
>>  					 DFSDM_DMA_BUFFER_SIZE,
>> @@ -1509,7 +1513,16 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
>>  	init_completion(&adc->completion);
>>  
>>  	/* Optionally request DMA */
>> -	if (stm32_dfsdm_dma_request(indio_dev)) {
>> +	ret = stm32_dfsdm_dma_request(indio_dev);
>> +	if (ret) {
>> +		if (ret != -ENODEV) {
>> +			if (ret != -EPROBE_DEFER)
>> +				dev_err(&indio_dev->dev,
>> +					"DMA channel request failed with %d\n",
>> +					ret);
>> +			return ret;
>> +		}
>> +
>>  		dev_dbg(&indio_dev->dev, "No DMA support\n");
>>  		return 0;
>>  	}
>>

- Péter

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