linux-kernel - Re: [PATCH 1/4] gpiolib: cdev: Flag invalid GPIOs as used

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Date:   Mon, 7 Dec 2020 15:16:50 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-team@...roid.com
Subject: Re: [PATCH 1/4] gpiolib: cdev: Flag invalid GPIOs as used

On Fri, Dec 04, 2020 at 04:47:36PM +0000, Marc Zyngier wrote:
> When reporting the state of a GPIO to userspace, we never check
> for the actual validity of the line, meaning we report invalid
> lines as being usable. A subsequent request will fail though,
> which is an inconsistent behaviour from a userspace perspective.
> 
> Instead, let's check for the validity of the line and report it
> as used if it is invalid. This allows a tool such as gpioinfo
> to report something sensible:
> 
> gpiochip3 - 4 lines:
> 	line   0:      unnamed       unused   input  active-high
> 	line   1:      unnamed       kernel   input  active-high [used]
> 	line   2:      unnamed       kernel   input  active-high [used]
> 	line   3:      unnamed       unused   input  active-high
> 
> In this example, lines 1 and 2 are invalid, and cannot be used by
> userspace.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  drivers/gpio/gpiolib-cdev.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index e9faeaf65d14..a0fcb4ccaa02 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -1910,6 +1910,7 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
>  	    test_bit(FLAG_USED_AS_IRQ, &desc->flags) ||
>  	    test_bit(FLAG_EXPORT, &desc->flags) ||
>  	    test_bit(FLAG_SYSFS, &desc->flags) ||
> +	    !gpiochip_line_is_valid(gc, info->offset) ||
>  	    !ok_for_pinctrl)
>  		info->flags |= GPIO_V2_LINE_FLAG_USED;

So this is somewhat separate from the rest of the series in case it
applies also to gpio chips with reserved ranges (e.g.
"gpio-reserved-ranges" devicetree property). Are they currently reported
as available?

Looks like this will work well also for USB gpio controllers with static
muxing configured in EEPROM, especially as that is how we already report
pins reported as unavailable by pinctrl (i.e. ok_for_pinctrl).

Johan