Re: [PATCH V2] gpio: rcar: Fix level interrupt handling

From: Valentine <valentine.barshak@cogentembedded.com>
To: linux-sh@vger.kernel.org, linux-gpio@vger.kernel.org
Cc: Simon Horman <horms@verge.net.au>,
	Magnus Damm <magnus.damm@gmail.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH V2] gpio: rcar: Fix level interrupt handling
Date: Mon, 09 Dec 2013 19:25:00 +0000	[thread overview]
Message-ID: <52A6190C.200@cogentembedded.com> (raw)
In-Reply-To: <1385748249-27170-1-git-send-email-valentine.barshak@cogentembedded.com>

On 11/29/2013 10:04 PM, Valentine Barshak wrote:
> According to the manual, if a port is set for level detection using
> the corresponding bit in the edge/level select register and an external
> level interrupt signal is asserted, the corresponding bit in INTDT
> does not use the FF to hold the input.
> Thus, writing 1 to the corresponding bits in INTCLR cannot clear the
> corresponding bits in the INTDT register. Instead, when an external
> input signal is stopped, the corresponding bit in INTDT is cleared
> automatically.
>
> Since the INTDT bit cannot be cleared for the level interrupts until
> the interrupt signal is stopped, we end up with the infinite loop
> when using deferred (threaded) IRQ handling.
>
> Since a deferred interrupt is disabled by the low-level handler and
> re-enabled only when the deferred handler is completed, Fix the issue
> by dropping disabled interrupts from the pending mask as suggested by
> Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>
> Changes in V2:
> * Drop disabled interrupts from pending mask altogether instead of
>    dropping level interrupts one by one once they get handled.
>
> Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
> ---
>   drivers/gpio/gpio-rcar.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-rcar.c b/drivers/gpio/gpio-rcar.c
> index d3f15ae..fd2d827 100644
> --- a/drivers/gpio/gpio-rcar.c
> +++ b/drivers/gpio/gpio-rcar.c
> @@ -169,7 +169,8 @@ static irqreturn_t gpio_rcar_irq_handler(int irq, void *dev_id)
>   	u32 pending;
>   	unsigned int offset, irqs_handled = 0;
>
> -	while ((pending = gpio_rcar_read(p, INTDT))) {
> +	while ((pending = gpio_rcar_read(p, INTDT) &
> +			  gpio_rcar_read(p, INTMSK))) {
>   		offset = __ffs(pending);
>   		gpio_rcar_write(p, INTCLR, BIT(offset));
>   		generic_handle_irq(irq_find_mapping(p->irq_domain, offset));
>

Laurent, Magnus,
do you have any concerns about fixing the level IRQ's as proposed here?

I'm more inclined to re-read the registers instead of caching the pending value
  pending = gpio_rcar_read(p, INTDT) & gpio_rcar_read(p, INTMSK));
and dropping bits inside the while loop
  pending &= ~BIT(offset);

I think this could help to catch new interrupts while processing previous ones.
It also makes minimum change to the original logic.

Please let me know if you think it's not good enough and the cached "pending" value
(or any other approach) should be used instead.

Thanks,
Val.