From 0769746183caff9d4334be48c7b0e7d2ec8716c4 Mon Sep 17 00:00:00 2001 From: Jani Nikula Date: Tue, 15 Dec 2009 16:46:20 -0800 Subject: gpiolib: add support for changing value polarity in sysfs Drivers may use gpiolib sysfs as part of their public user space interface. The GPIO number and polarity might change from board to board. The gpio_export_link() call can be used to hide the GPIO number from user space. Add support for also hiding the GPIO line polarity changes from user space. Signed-off-by: Jani Nikula Cc: David Brownell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/gpio.txt | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'Documentation/gpio.txt') diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index e4e7daed2ba..1866c27eec6 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -531,6 +531,13 @@ and have the following read/write attributes: This file exists only if the pin can be configured as an interrupt generating input pin. + "active_low" ... reads as either 0 (false) or 1 (true). Write + any nonzero value to invert the value attribute both + for reading and writing. Existing and subsequent + poll(2) support configuration via the edge attribute + for "rising" and "falling" edges will follow this + setting. + GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the controller implementing GPIOs starting at #42) and have the following read-only attributes: @@ -566,6 +573,8 @@ requested using gpio_request(): int gpio_export_link(struct device *dev, const char *name, unsigned gpio) + /* change the polarity of a GPIO node in sysfs */ + int gpio_sysfs_set_active_low(unsigned gpio, int value); After a kernel driver requests a GPIO, it may only be made available in the sysfs interface by gpio_export(). The driver can control whether the @@ -580,3 +589,9 @@ After the GPIO has been exported, gpio_export_link() allows creating symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can use this to provide the interface under their own device in sysfs with a descriptive name. + +Drivers can use gpio_sysfs_set_active_low() to hide GPIO line polarity +differences between boards from user space. This only affects the +sysfs interface. Polarity change can be done both before and after +gpio_export(), and previously enabled poll(2) support for either +rising or falling edge will be reconfigured to follow this setting. -- cgit v1.2.3-70-g09d2