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897396b418
GPIO chips often have data input and output registers aliased to the same offset. The output register is non-valitile and could in theory be cached. The input register however is volatile by nature and hence should not be cached, resulting in different requirements for reads and writes. The generic gpio chip implementation stores a shadow value of the pin output data, which is updated and written to hardware on output data changes in bgpio_set(), bgpio_set_set(). Pin input values are always obtained by reading the aliased data register from hardware. For gpio-regmap the situation is more complex as the output data could be in multiple registers, but we can use the regmap cache to shadow the output values when marking the data registers as non-volatile. By using regmap_read_bypassed() we can still treat the input values as volatile, irrespective of the regmap config. This ensures proper functioning of writing the output register with regmap_write_bits(), which will then use and update the cache only on data writes, gaining some performance from the cached output values. Signed-off-by: Sander Vanheule <sander@svanheule.net> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Reviewed-by: Michael Walle <mwalle@kernel.org> Link: https://lore.kernel.org/r/20251021142407.307753-3-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.