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

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Date:   Tue, 24 Dec 2019 00:00:30 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>,
        <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>
Subject: Re: [PATCH] iio: adc: stm32-dfsdm: Use dma_request_chan() instead
 dma_request_slave_channel()

Hi Jonathan,

On 12/23/19 5:45 PM, Jonathan Cameron wrote:
> On Tue, 17 Dec 2019 09:52:21 +0200
> Peter Ujfalusi <peter.ujfalusi@...com> 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>
> I don't think this one goes far enough.  
> 
> One of the paths does:
> 
> 	/* Optionally request DMA */
> 	if (stm32_dfsdm_dma_request(indio_dev)) {
> 		dev_dbg(&indio_dev->dev, "No DMA support\n");
> 		return 0;
> 	}
> 
> That needs specific handling for deferred probing.

Right, I have checked the stm32_dfsdm_audio_init() path, via that the
error is propagated correctly.

I'll send an update next year ;)

> 
>> ---
>>  drivers/iio/adc/stm32-dfsdm-adc.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
>> index e493242c266e..3aac1a21f9d0 100644
>> --- a/drivers/iio/adc/stm32-dfsdm-adc.c
>> +++ b/drivers/iio/adc/stm32-dfsdm-adc.c
>> @@ -1383,9 +1383,9 @@ 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))
>> +		return PTR_ERR(adc->dma_chan);
>>  
>>  	adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
>>  					 DFSDM_DMA_BUFFER_SIZE,
> 

- Peter

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