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

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Date:   Mon, 23 Dec 2019 15:45:38 +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>
Subject: Re: [PATCH] iio: adc: stm32-dfsdm: Use dma_request_chan() instead
 dma_request_slave_channel()

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.

> ---
>  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,