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ed2bd02d24
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>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.