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

[Marc Zyngier <maz@kernel.org>]

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@kernel.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?

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...