Re: [PATCH] iio: adc: at91: disable adc channel interrupt in timeout case

From: Jonathan Cameron <jic23@kernel.org>
To: <g.ottinger@abatec.at>
Cc: <eugen.hristev@microchip.com>, <s.etzlstorfer@abatec.at>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Ludovic Desroches <ludovic.desroches@microchip.com>,
	"David S. Miller" <davem@davemloft.net>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Kees Cook <keescook@chromium.org>, <linux-iio@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	Maxime Ripard <maxime.ripard@bootlin.com>
Subject: Re: [PATCH] iio: adc: at91: disable adc channel interrupt in timeout case
Date: Sat, 2 Feb 2019 10:20:48 +0000	[thread overview]
Message-ID: <20190202102021.12bb0a72@archlinux> (raw)
In-Reply-To: <20190130134202.5831-1-g.ottinger@abatec.at>

On Wed, 30 Jan 2019 14:42:02 +0100
<g.ottinger@abatec.at> wrote:

> From: Georg Ottinger <g.ottinger@abatec.at>
> 
> Having a brief look at at91_adc_read_raw() it is obvious that in the case
> of a timeout the setting of AT91_ADC_CHDR and AT91_ADC_IDR registers is
> omitted. If 2 different channels are queried we can end up with a
> situation where two interrupts are enabled, but only one interrupt is
> cleared in the interrupt handler. Resulting in a interrupt loop and a
> system hang.
> 
> Signed-off-by: Georg Ottinger <g.ottinger@abatec.at>

Whilst I agree this looks like a correct change, I would like Maxime
to take a look as he is obviously much more familiar with the driver
than I am.

I suspect you can only actually get there in the event of a hardware
failure as that isn't actually a timeout you should ever see.
Could be wrong though!

Thanks,

Jonathan

> ---
>  drivers/iio/adc/at91_adc.c | 28 +++++++++++++++++-----------
>  1 file changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index 75d2f7358..596841a3c 100644
> --- a/drivers/iio/adc/at91_adc.c
> +++ b/drivers/iio/adc/at91_adc.c
> @@ -704,23 +704,29 @@ static int at91_adc_read_raw(struct iio_dev *idev,
>  		ret = wait_event_interruptible_timeout(st->wq_data_avail,
>  						       st->done,
>  						       msecs_to_jiffies(1000));
> -		if (ret == 0)
> -			ret = -ETIMEDOUT;
> -		if (ret < 0) {
> -			mutex_unlock(&st->lock);
> -			return ret;
> -		}
> -
> -		*val = st->last_value;
>  
> +		/* Disable interrupts, regardless if adc conversion was
> +		 * successful or not
> +		 */
>  		at91_adc_writel(st, AT91_ADC_CHDR,
>  				AT91_ADC_CH(chan->channel));
>  		at91_adc_writel(st, AT91_ADC_IDR, BIT(chan->channel));
>  
> -		st->last_value = 0;
> -		st->done = false;
> +		if (ret > 0) {
> +			/* a valid conversion took place */
> +			*val = st->last_value;
> +			st->last_value = 0;
> +			st->done = false;
> +			ret = IIO_VAL_INT;
> +		} else if (ret == 0) {
> +			/* conversion timeout */
> +			dev_err(&idev->dev, "ADC Channel %d timeout.\n",
> +				chan->channel);
> +			ret = -ETIMEDOUT;
> +		}
> +
>  		mutex_unlock(&st->lock);
> -		return IIO_VAL_INT;
> +		return ret;
>  
>  	case IIO_CHAN_INFO_SCALE:
>  		*val = st->vref_mv;