linux-kernel - Re: [PATCH v2 1/2] iio: adc: at91: fix acking DRDY irq on simple conversions

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Date:   Mon, 24 Sep 2018 21:23:33 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Eugen Hristev <eugen.hristev@...rochip.com>
Cc:     <ludovic.desroches@...rochip.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <nicolas.ferre@...rochip.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>
Subject: Re: [PATCH v2 1/2] iio: adc: at91: fix acking DRDY irq on simple
 conversions

On Mon, 24 Sep 2018 10:51:43 +0300
Eugen Hristev <eugen.hristev@...rochip.com> wrote:

> When doing simple conversions, the driver did not acknowledge the DRDY irq.
> If this irq status is not acked, it will be left pending, and as soon as a
> trigger is enabled, the irq handler will be called, it doesn't know why
> this status has occurred because no channel is pending, and then it will go
> int a irq loop and board will hang.
> To avoid this situation, read the LCDR after a raw conversion is done.
> 
> Fixes 0e589d5fb ("ARM: AT91: IIO: Add AT91 ADC driver.")
> Cc: Maxime Ripard <maxime.ripard@...tlin.com>
> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> ---
> Hello Jonathan,
> 
> I moved this LCDR read/acknowledge into the IRQ handler after the conversion
> value is being read.
Ah.. This all makes more sense now. I'd misunderstood originally and thought
we were looking at a read raw that wasn't using the interrupt at all.

Sorry about that.

However, mostly by coincidence (given I misread the code) I think
this is a neater way to do this than the previous option as it
puts it near the actual read.

Given Maxime is the author of this one though I'd like to leave it
on the list a little longer before applying.

At this stage in the cycle I'll probably just queue it up for the
next merge window anyway (marked for stable). It's not exactly a new bug
after all.

Thanks,

Jonathan
> Sorry about the noise to stable@...r, removed from message.
> 
> Thanks,
> Eugen
> 
>  drivers/iio/adc/at91_adc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index 44b5168..e3be88e 100644
> --- a/drivers/iio/adc/at91_adc.c
> +++ b/drivers/iio/adc/at91_adc.c
> @@ -279,6 +279,8 @@ static void handle_adc_eoc_trigger(int irq, struct iio_dev *idev)
>  		iio_trigger_poll(idev->trig);
>  	} else {
>  		st->last_value = at91_adc_readl(st, AT91_ADC_CHAN(st, st->chnb));
> +		/* Needed to ACK the DRDY interruption */
> +		at91_adc_readl(st, AT91_ADC_LCDR);
>  		st->done = true;
>  		wake_up_interruptible(&st->wq_data_avail);
>  	}