Re: [PATCH] pinctrl: bcm2835: Use bcm2835 gpio_chip label for bcm2711

[Lukas Wunner <lukas@wunner.de>]

On Tue, Feb 15, 2022 at 09:17:49AM -0800, Florian Fainelli wrote:
> >>> Am 15.02.22 um 06:52 schrieb Lukas Wunner:
> >>>> Commit b1d84a3d0a26 ("pinctrl: bcm2835: Add support for all GPIOs on
> >>>> BCM2711") used a different label for the bcm2711 gpio_chip vis-à-vis
> >>>> the bcm2835.
[...]
> I agree with Stefan here, besides changing the driver name now would
> mean potentially breaking user-space since the driver name is visible in
> a variety of places. Seems to me like this is too late, we should have
> caught this during the introduction of 2711.

This isn't about the driver name but the gpio_chip label.

The .name attribute of bcm2711_pinctrl_desc and bcm2711_pinctrl_gpio_range
is only visible in debugfs, which doesn't count as user-space ABI.

The .label attribute of bcm2711_gpio_chip is indeed visible in sysfs
and could in theory be used by udev rules, though I doubt it.

It definitely was a mistake not to use the same label as pinctrl-bcm2835.
Using a different label hinges on the notion that it's a different chip,
and while that may apply for the 4B+ and CM4, the assumption falls apart
with the CM4S which seeks to be a drop-in replacement for CM1/CM3,
but really is not because of mistakes like this one.  We're likely
not the only ones bitten by this, just the first to report.

Thanks,

Lukas