path: root/Documentation/pinctrl.txt
diff options
authorLinus Walleij <linus.walleij@linaro.org>2011-11-14 09:06:22 (GMT)
committerLinus Walleij <linus.walleij@linaro.org>2012-01-03 08:10:01 (GMT)
commit542e704f3ffee1dc4539c9e8191e4dc215220f5e (patch)
treeda2f8aae8bedb6e3216b4808dc743eb94c3270e3 /Documentation/pinctrl.txt
parent75d6642a3ee1dfe2552028997cdcc2c4207bec8f (diff)
pinctrl: GPIO direction support for muxing
When requesting a single GPIO pin to be muxed in, some controllers will need to poke a different value into the control register depending on whether the pin will be used for GPIO output or GPIO input. So create pinmux counterparts to gpio_direction_[input|output] in the pinctrl framework. ChangeLog v1->v2: - This also amends the documentation to make it clear the this function and associated machinery is *ONLY* intended as a backend to gpiolib machinery, not for everyone and his dog to start playing around with pins. ChangeLog v2->v3: - Don't pass an argument to the common request function, instead provide pinmux_* counterparts to the gpio_direction_[input|output] calls, simpler and anyone can understand it. ChangeLog v3->v4: - Fix numerous spelling mistakes and dangling text in documentation. Add Ack and Rewewed-by. Cc: Igor Grinberg <grinberg@compulab.co.il> Acked-by: Stephen Warren <swarren@nvidia.com> Reviewed-by: Thomas Abraham <thomas.abraham@linaro.org> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'Documentation/pinctrl.txt')
1 files changed, 24 insertions, 8 deletions
diff --git a/Documentation/pinctrl.txt b/Documentation/pinctrl.txt
index 43ba411..3846264 100644
--- a/Documentation/pinctrl.txt
+++ b/Documentation/pinctrl.txt
@@ -645,6 +645,17 @@ All the above functions are mandatory to implement for a pinmux driver.
Pinmux interaction with the GPIO subsystem
+The public pinmux API contains two functions named pinmux_request_gpio()
+and pinmux_free_gpio(). These two functions shall *ONLY* be called from
+gpiolib-based drivers as part of their gpio_request() and
+gpio_free() semantics. Likewise the pinmux_gpio_direction_[input|output]
+shall only be called from within respective gpio_direction_[input|output]
+gpiolib implementation.
+NOTE that platforms and individual drivers shall *NOT* request GPIO pins to be
+muxed in. Instead, implement a proper gpiolib driver and have that driver
+request proper muxing for its pins.
The function list could become long, especially if you can convert every
individual pin into a GPIO pin independent of any other pins, and then try
the approach to define every pin as a function.
@@ -652,19 +663,24 @@ the approach to define every pin as a function.
In this case, the function array would become 64 entries for each GPIO
setting and then the device functions.
-For this reason there is an additional function a pinmux driver can implement
-to enable only GPIO on an individual pin: .gpio_request_enable(). The same
-.free() function as for other functions is assumed to be usable also for
-GPIO pins.
+For this reason there are two functions a pinmux driver can implement
+to enable only GPIO on an individual pin: .gpio_request_enable() and
This function will pass in the affected GPIO range identified by the pin
controller core, so you know which GPIO pins are being affected by the request
-Alternatively it is fully allowed to use named functions for each GPIO
-pin, the pinmux_request_gpio() will attempt to obtain the function "gpioN"
-where "N" is the global GPIO pin number if no special GPIO-handler is
+If your driver needs to have an indication from the framework of whether the
+GPIO pin shall be used for input or output you can implement the
+.gpio_set_direction() function. As described this shall be called from the
+gpiolib driver and the affected GPIO range, pin offset and desired direction
+will be passed along to this function.
+Alternatively to using these special functions, it is fully allowed to use
+named functions for each GPIO pin, the pinmux_request_gpio() will attempt to
+obtain the function "gpioN" where "N" is the global GPIO pin number if no
+special GPIO-handler is registered.
Pinmux board/machine configuration

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