linux-kernel - Re: [PATCH v3] iio: adc: stm32-adc: Use dma_request_chan() instead dma_request_slave

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Date:   Sat, 11 Jan 2020 11:00:39 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>,
        <fabrice.gasnier@...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 v3] iio: adc: stm32-adc: Use dma_request_chan() instead
 dma_request_slave_channel()

On Wed, 8 Jan 2020 10:08:01 +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>
> Acked-by: Fabrice Gasnier <fabrice.gasnier@...com>

Applied to the togreg branch of iio.git and pushed out as testing.

thanks,

Jonathan

> ---
> Hi,
> 
> Changes since v2:
> - Replace the comment as suggested by Fabrice
> 
> Changes since v1:
> - Fall back to IRQ mode only in case of ENODEV
> 
> Regards,
> Peter
> 
>  drivers/iio/adc/stm32-adc.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index 3b291d72701c..a8d2414ee2eb 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -1746,9 +1746,21 @@ static int stm32_adc_dma_request(struct iio_dev *indio_dev)
>  	struct dma_slave_config config;
>  	int ret;
>  
> -	adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx");
> -	if (!adc->dma_chan)
> +	adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx");
> +	if (IS_ERR(adc->dma_chan)) {
> +		ret = PTR_ERR(adc->dma_chan);
> +		if (ret != -ENODEV) {
> +			if (ret != -EPROBE_DEFER)
> +				dev_err(&indio_dev->dev,
> +					"DMA channel request failed with %d\n",
> +					ret);
> +			return ret;
> +		}
> +
> +		/* DMA is optional: fall back to IRQ mode */
> +		adc->dma_chan = NULL;
>  		return 0;
> +	}
>  
>  	adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev,
>  					 STM32_DMA_BUFFER_SIZE,