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

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Date:   Mon, 23 Dec 2019 15:42:30 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
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>,
        Fabrice Gasnier <fabrice.gasnier@...com>
Subject: Re: [PATCH] iio: adc: stm32-adc: Use dma_request_chan() instead
 dma_request_slave_channel()

On Tue, 17 Dec 2019 09:51:53 +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>
Hi Peter,

Change looks sensible to me, but I'd like to leave a little longer
for others to look at this.

Give me a poke if I seem to have lost it by the end of the first
week in Jan.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/stm32-adc.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index 3b291d72701c..5dab23f1fdee 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -1746,9 +1746,15 @@ 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)) {
> +		if (PTR_ERR(adc->dma_chan) == -EPROBE_DEFER)
> +			return -EPROBE_DEFER;
> +
> +		/* Ignore errors to 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,