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If gpiolib is disabled, we use the inline stubs from gpio/consumer.h instead of regular definitions of GPIO API. The stubs for 'optional' variants of gpiod_get routines return NULL in this case as if the relevant GPIO wasn't found. This is correct so far. Calling other (non-gpio_get) stubs from this header triggers a warning because the GPIO descriptor couldn't have been requested. The warning however is unconditional (WARN_ON(1)) and is emitted even if the passed descriptor pointer is NULL. We don't want to force the users of 'optional' gpio_get to check the returned pointer before calling e.g. gpiod_set_value() so let's only WARN on non-NULL descriptors. Cc: stable@vger.kernel.org Reported-by: Claus H. Stovgaard <cst@phaseone.com> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
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 Restructured Text 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.