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gpio: Clarify consumer stubs use-cases 

After discussion we add a few blurbs to clarify how the stubs
in the consumer API are supposed to be used.

Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Linus Walleij 2017-09-12 09:32:34 +02:00
parent aa5c2a88bb
commit a621c99a96
1 changed files with 19 additions and 3 deletions
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22
Documentation/gpio/consumer.txt
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@ -10,14 +10,30 @@ Guidelines for GPIOs consumers
==============================
Drivers that can't work without standard GPIO calls should have Kconfig entries
that depend on GPIOLIB. The functions that allow a driver to obtain and use
GPIOs are available by including the following file:
that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
obtain and use GPIOs are available by including the following file:
#include <linux/gpio/consumer.h>
There are static inline stubs for all functions in the header file in the case
where GPIOLIB is disabled. When these stubs are called they will emit
warnings. These stubs are used for two use cases:
- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
the current platform does not enable or select GPIOLIB because we are not
going to execute the system anyway.
- Truly optional GPIOLIB support - where the driver does not really make use
of the GPIOs on certain compile-time configurations for certain systems, but
will use it under other compile-time configurations. In this case the
consumer must make sure not to call into these functions, or the user will
be met with console warnings that may be perceived as intimidating.
All the functions that work with the descriptor-based GPIO interface are
prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
other function in the kernel should use these prefixes.
other function in the kernel should use these prefixes. The use of the legacy
functions is strongly discouraged, new code should use <linux/gpio/consumer.h>
and descriptors exclusively.
Obtaining and Disposing GPIOs