Re: "leds: gpio: Use generic support for composing LED names" breaks gpio debugfs

Jacek Anaszewski
2019-12-04T20:52:57Z

Hi Russel,

On 12/4/19 12:02 PM, Russell King - ARM Linux admin wrote:
> Hi,
>
> Patch d7235f5feaa0 ("leds: gpio: Use generic support for composing LED
> names") changed the way labels are used.
>
> devm_fwnode_get_gpiod_from_child() is passed led.name, which used to be
> set to the label or node name, resulting in /sys/kernel/debug/gpio
> containing useful information. For example:
>
> gpio-487 ( |udpu:green:power ) out lo
> gpio-488 ( |udpu:red:power ) out hi
> gpio-489 ( |udpu:green:network ) out hi
> gpio-490 ( |udpu:red:network ) out hi
> gpio-491 ( |udpu:green:alarm ) out hi
> gpio-492 ( |udpu:red:alarm ) out hi
>
> After this commit, it now contains a rather less useful:
>
> gpio-487 ( |? ) out hi ACTIVE LOW
> gpio-488 ( |? ) out hi ACTIVE LOW
> gpio-489 ( |? ) out hi ACTIVE LOW
> gpio-490 ( |? ) out hi ACTIVE LOW
> gpio-491 ( |? ) out hi ACTIVE LOW
> gpio-492 ( |? ) out hi ACTIVE LOW
>
> This is because led.name is now NULL prior to the call to
> devm_fwnode_get_gpiod_from_child().

Ugh, my bad. But it actually has been wrong since the patch
a96aa64cb5723 ("leds/led-class: Handle LEDs with the same name"),
which enabled LED core to amend the LED name just beforehand
the registration of a LED class device.

It seem that the only proper solution would be introducing a new
pre_register_cdev(const char *name) op to the LED core, that would allow
drivers to come up with their implementation thereof. In this particular
case leds-gpio driver would need to put there gpiod initialization.

The pre_register_device op would need to be called (when available)
from the led_classdev_register_ext() after calling
led_classdev_next_name() and before device_create_with_groups().
The op would have to be passed the final_name variable then.

> While this is not an API, it is useful for debugging, and given the
> dynamic allocation of GPIOs to physical GPIOs, having the labels
> present is an advantage.
>
> Can this be fixed / old behaviour restored?

If there are no objections I can come up with a fix, but no
sooner than at the weekend.

--
Best regards,
Jacek Anaszewski