linux-kernel - Re: [PATCH 2/2] iio: at91-sama5d2: Limit requested watermark value to hwfifo size

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Message-ID: <20220122170447.68f35cfa@jic23-huawei>
Date:   Sat, 22 Jan 2022 17:04:47 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Eugen Hristev <eugen.hristev@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>
Subject: Re: [PATCH 2/2] iio: at91-sama5d2: Limit requested watermark value
 to hwfifo size

On Mon, 17 Jan 2022 10:25:12 +0000
Paul Cercueil <paul@...pouillou.net> wrote:

> Instead of returning an error if the watermark value is too high, which
> the core will silently ignore anyway, limit the value to the hardware
> FIFO size; a lower-than-requested value is still better than using the
> default, which is usually 1.

There is another potential error condition in this function which will
also be ignored by the core.

As such whilst I agree this is a sensible thing to do in this
particular case I think we should also be handling the error in the core.

I think it would be better to clean that up at the same time
as these improvements - particularly as I'd guess you have a convenient
test setup to check the error unwind is correct?

Thanks,

Jonathan

> 
> Cc: Eugen Hristev <eugen.hristev@...rochip.com>
> Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>
> Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Cc: Ludovic Desroches <ludovic.desroches@...rochip.com>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/iio/adc/at91-sama5d2_adc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
> index 854b1f81d807..5cc84f4a17bb 100644
> --- a/drivers/iio/adc/at91-sama5d2_adc.c
> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
> @@ -1752,7 +1752,7 @@ static int at91_adc_set_watermark(struct iio_dev *indio_dev, unsigned int val)
>  	int ret;
>  
>  	if (val > AT91_HWFIFO_MAX_SIZE)
> -		return -EINVAL;
> +		val = AT91_HWFIFO_MAX_SIZE;
>  
>  	if (!st->selected_trig->hw_trig) {
>  		dev_dbg(&indio_dev->dev, "we need hw trigger for DMA\n");