linux-kernel - Re: [PATCH v2] iio: adc: at91-sama5d2_adc: Use dma_request_chan() instead dma_request_slave

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Message-ID: <20191223155001.3c4c7261@archlinux>
Date:   Mon, 23 Dec 2019 15:50:01 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     <vkoul@...nel.org>, <ludovic.desroches@...rochip.com>,
        <eugen.hristev@...rochip.com>, <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iio: adc: at91-sama5d2_adc: Use dma_request_chan()
 instead dma_request_slave_channel()

On Tue, 17 Dec 2019 12:31:00 +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.
Unfortunately that doesn't seem to be true.
The function in question returns void...

And for that matter is called only from the set_watermark callback which
doesn't run at probe time.

So if we were to get a deferred response at runtime there isn't a whole
lot we could do with it.

Jonathan



> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
> Hi,
> 
> Changes since v1:
> - Subject prefix is corrected to "iio: adc: at91-sama5d2_adc:"
> 
> Regards,
> Peter
> 
>  drivers/iio/adc/at91-sama5d2_adc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
> index e1850f3d5cf3..a5c7771227d5 100644
> --- a/drivers/iio/adc/at91-sama5d2_adc.c
> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
> @@ -1444,10 +1444,10 @@ static void at91_adc_dma_init(struct platform_device *pdev)
>  	if (st->dma_st.dma_chan)
>  		return;
>  
> -	st->dma_st.dma_chan = dma_request_slave_channel(&pdev->dev, "rx");
> -
> -	if (!st->dma_st.dma_chan)  {
> +	st->dma_st.dma_chan = dma_request_chan(&pdev->dev, "rx");
> +	if (IS_ERR(st->dma_st.dma_chan))  {
>  		dev_info(&pdev->dev, "can't get DMA channel\n");
> +		st->dma_st.dma_chan = NULL;
>  		goto dma_exit;
>  	}
>