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-rw-r--r--Documentation/gpio/consumer.txt22
1 files changed, 19 insertions, 3 deletions
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 912568baabb9..ddbfa775a78a 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -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