gpio: regmap: Force writes for aliased data regs

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GPIO chips often have data input and output fields aliased to the same
offset. Since gpio-regmap performs a value update before the direction
update (to prevent glitches), a pin currently configured as input may
cause regmap_update_bits() to not perform a write.

This may cause unexpected line states when the current input state
equals the requested output state:

        OUT   IN      OUT
    DIR ''''''\...|.../''''''

    pin ....../'''|'''\......
             (1) (2) (3)

    1. Line was configurad as out-low, but is reconfigured to input.
       External logic results in high value.
    2. Set output value high. regmap_update_bits() sees the value is
       already high and discards the register write.
    3. Line is switched to output, maintaining the stale output config
       (low) instead of the requested config (high).

By switching to regmap_write_bits(), a write of the requested output
value can be forced, irrespective of the read state. Do this only for
aliased registers, so the more efficient regmap_update_bits() can still
be used for distinct registers.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
Reviewed-by: Michael Walle <mwalle@kernel.org>
Link: https://lore.kernel.org/r/20251021142407.307753-2-sander@svanheule.net
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

...

This commit is contained in:

Sander Vanheule 2025-10-21 16:23:56 +02:00 • committed by Bartosz Golaszewski

parent d5376026f9

commit ed2bd02d24

1 changed files with 9 additions and 3 deletions

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drivers/gpio/gpio-regmap.c

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