Re: [PATCH] iio: adc: ti_am335x_adc: Make DMAs optional

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 14 Sep 2023 14:13:00 +0200
Wadim Egorov <w.egorov@phytec.de> wrote:

> DMAs are optional. Even if the DMA request is unsuccessfully,
> the ADC can still work properly.

> Make tiadc_request_dma() not fail if we do not provide dmas &
> dma-names properties.
> 
> This actually fixes the wrong error handling of the tiadc_request_dma()
> result where the probing only failed if -EPROPE_DEFER was returned.
> 
> Fixes: f438b9da75eb ("drivers: iio: ti_am335x_adc: add dma support")
> 
No line break here.  Fixes tag is part of the main tag block.
> Signed-off-by: Wadim Egorov <w.egorov@phytec.de>


> ---
>  drivers/iio/adc/ti_am335x_adc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
> index 8db7a01cb5fb..e14aa9254ab1 100644
> --- a/drivers/iio/adc/ti_am335x_adc.c
> +++ b/drivers/iio/adc/ti_am335x_adc.c
> @@ -543,8 +543,11 @@ static int tiadc_request_dma(struct platform_device *pdev,
>  	if (IS_ERR(dma->chan)) {
>  		int ret = PTR_ERR(dma->chan);
>  
> +		if (ret != -ENODEV)
> +			return dev_err_probe(&pdev->dev, ret,
> +					     "RX DMA channel request failed\n");
>  		dma->chan = NULL;
> -		return ret;
> +		return 0;
>  	}
>  
>  	/* RX buffer */
> @@ -670,7 +673,7 @@ static int tiadc_probe(struct platform_device *pdev)
>  	platform_set_drvdata(pdev, indio_dev);
>  
>  	err = tiadc_request_dma(pdev, adc_dev);
> -	if (err && err == -EPROBE_DEFER)
> +	if (err)

So this looks like a more subtle change than you are describing.
In the original code, we backed off only if the return was a PROBE_DEFER, otherwise
we carried on.

Your change seems to make that happen for any non -ENODEV error, including PROBE_DEFER.
That's fine, but it's not what the description implies.

Whilst tiadc_request_dma will fail today if the dmas etc is not provided, that seems
like correct behavior to me.  A function requesting dma fails if it isn't available.
The handling of whether to carry on the job for the caller.

So I think it should just be
	if (err && err != -EINVAL)
		goto err_dma;

and no change in tiadc_request_dma()

However, the case you describe should have worked find with existing code
as it wasn't -EPROBE_DEFER, so I don't understand why you were looking at this
code block in the first place?

Jonathan


>  		goto err_dma;
>  
>  	return 0;