Re: [PATCH] gpio: fix locking open drain IRQ lines

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Wed, May 27, 2020 at 04:07:58PM +0200, Linus Walleij wrote:
> We provided the right semantics on open drain lines being
> by definition output but incidentally the irq set up function
> would only allow IRQs on lines that were "not output".
> 
> Fix the semantics to allow output open drain lines to be used
> for IRQs.
> 
> Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: stable@vger.kernel.org
> Fixes: 256efaea1fdc ("gpiolib: fix up emulated open drain outputs")

As I've pointed out in the reporting thread, I don't think it can be
justified as a regression - it's a bug in its own right that has been
discovered by unifying the gpiolib semantics, since the cec-gpio code
will fail on hardware that can provide real open-drain outputs
irrespective of that commit.

So, you're really fixing a deeper problem that was never discovered
until gpiolib's semantics were fixed to be more uniform.

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>  drivers/gpio/gpiolib.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index b4b5792fe2ff..edd74ff31cea 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -4220,7 +4220,9 @@ int gpiochip_lock_as_irq(struct gpio_chip *gc, unsigned int offset)
>  		}
>  	}
>  
> -	if (test_bit(FLAG_IS_OUT, &desc->flags)) {
> +	/* To be valid for IRQ the line needs to be input or open drain */
> +	if (test_bit(FLAG_IS_OUT, &desc->flags) &&
> +	    !test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {
>  		chip_err(gc,
>  			 "%s: tried to flag a GPIO set as output for IRQ\n",
>  			 __func__);
> -- 
> 2.25.4
> 
> 

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