Subject: Re: [PATCH v2] iio: adc: stm32-dfsdm: Use dma_request_chan() instead dma_request_slave_channel()

From: Jonathan Cameron <[email-masked]>
Date: Sat, 11 Jan 2020 10:58:04 +0000

On Thu, 9 Jan 2020 13:56:14 +0100
Fabrice Gasnier <[email-masked]> wrote:

> On 1/9/20 12:40 PM, Peter Ujfalusi wrote:
> > 
> > 
> > On 09/01/2020 13.29, Fabrice Gasnier wrote:  
> >> 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 <[email-masked]>
> >>>>> ---
> >>>>> 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 <[email-masked]>
> >>>>
> >>>>  
> >>>>>
> >>>>> 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,  
> > 
> > Hi Fabrice,
> >   
> >> 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.  
> > 
> > PTR_ERR(NULL); will return 0
> > I need to retrieve the actual error code before NULLing dma_chan.  
> 
> Oh yes, so please forget this.
> Thanks,
> Fabrice

Applied to the togreg branch of iio.git and pushed out as testing.
Note I'll need to rebase once Greg pushes out staging/staging-next
with the changes currently in staging/staging-testing.  Shouldn't
have an effect on this though!

Thanks,

Jonathan

> 
> >   
> >>  
> >>>  
> >>>>
> >>>> 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
> >>>
> >>> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> >>> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> >>>  
> > 
> > - Péter
> > 
> > Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> > Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> >   

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