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 12:29:01 +0100
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Peter Ujfalusi <peter.ujfalusi@...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 1/9/20 11:32 AM, Peter Ujfalusi wrote:
> 
> 
> 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.

Hi Peter,

Sorry I wasn't clear enough. I agree with you. I was suggesting only,
talking about the 'ret' variable. It may be removed to spare a few lines
:-).
	if (IS_ERR(adc->dma_chan)) {
		adc->dma_chan = NULL;
		return PTR_ERR(adc->dma_chan);
	}
I'm okay both ways.

> 
>>
>> 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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