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

[Marc Zyngier]

On 2020-12-07 14:16, Johan Hovold wrote:
> 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@xxxxxxxxxx>
> > ---
> >  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?

I don't have any HW that uses this, but gpiolib-of.c makes use of it to
expose the valid GPIO range. I expect these systems suffer from the same
issue.

> 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).

Thanks,

        M.
--
Jazz is not dead. It just smells funny...