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 10:13:02 +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 1/7/20 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.

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;
>  	}
>