Re: [PATCH v2] arm: gpio: Add set_flags callback to the Tegra gpio driver

["Łukasz Majewski" <lukma@nabladev.com>]

Hi Svyatoslav,

> пн, 22 вер. 2025 р. о 17:16 Lukasz Majewski <lukma@nabladev.com> пише:
> >
> > This patch adds support for the .set_flags callback.
> > For now following flags are supported:
> > - GPIOD_IS_AF (i.e. "alternate function").
> > - GPIOD_IS_IN
> > - GPIOD_IS_OUT
> >
> > Currently, the .set_flags in gpio-uclass.c (function
> > dm_gpio_set_value()) is used before .set_value callback, so
> > functionally replaces it. As a result the corresponding
> > tegra_gpio_set_value() can be removed.
> >
> > Signed-off-by: Lukasz Majewski <lukma@nabladev.com>
> > ---
> >
> > Changes for v2:
> > - Fix the format specifier for flags in debug() function
> > - Update commit message
> > - Remove tegra_gpio_set_value() method (as it is functionally
> > replaced by set_value()
> > - Prevent from returning errors when flags = 0 (problem with e.g.
> > I2C GPIO support)
> > ---
> >  drivers/gpio/tegra_gpio.c | 39
> > +++++++++++++++++++++++---------------- 1 file changed, 23
> > insertions(+), 16 deletions(-) 
> 
> Lukasz, thank you for this change I would really like to see it in
> mainline. ATM I have no capabilities to debug 

You mean test if it works?

> this and I will return
> to it but that may not be soon unfortunately.

This is a bit problematic for me, as:

1. Some future work depends on it (more details below).
2. The "set_flags()" callback seems like being now the one to be
advised to being implemented and used. 



Can you predict when you will be able to come back to this task? Is
this the matter of weeks or months?

> In case you really need
> switch GPIO back to SFIO and Linux cannot handle this, you an use
> dm_gpio_free to release gpios in board_preboot_os in the board as a
> temporary measure.

Yes, this is a temporary solution - i.e. dm_gpio_free() is supposed to
"free" the pin. IMHO, the set_flags() shall be used, as I in fact do
want to set the CFG_SFIO flag, not release the gpio.

> 
> Overall issue you are describing is not u-boot's it is kernels, kernel
> must reconfigure gpios for proper work regardless of their previous
> state. If it is not the case, then kernel device configuration is
> incomplete or wrong.

This is how the pinmux in Linux for Tegra is written. You can setup the
PAD parameters, but you cannot set the pin's function.

In other words - you have to do it in bootloader (u-boot in this case).

In my case - customer uses the pin in u-boot as GPIO to check carrier
board version, then the same pin in Linux is going to be used as
special function one.

Unfortunately, above "reconfiguration" cannot be done in Linux. 

As other "rework" of gpio code depends on it (use dm) - I would like to
postpone my work until this functionality is available in mainline (and
hence avoid "temporal solutions").

-- 
Best regards,

Lukasz Majewski

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