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Add a virtual GPIO proxy driver which arbitrates access to a single shared GPIO by multiple users. It works together with the core shared GPIO support from GPIOLIB and functions by acquiring a reference to a shared GPIO descriptor exposed by gpiolib-shared and making sure that the state of the GPIO stays consistent. In general: if there's only one user at the moment: allow it to do anything as if this was a normal GPIO (in essence: just propagate calls to the underlying real hardware driver). If there are more users: don't allow to change the direction set by the initial user, allow to change configuration options but warn about possible conflicts and finally: treat the output-high value as a reference counted, logical "GPIO enabled" setting, meaning: the GPIO value is set to high when the first user requests it to be high and back to low once the last user stops "voting" for high. Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Acked-by: Linus Walleij <linus.walleij@linaro.org> Link: https://lore.kernel.org/r/20251112-gpio-shared-v4-4-b51f97b1abd8@linaro.org Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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.