diff options
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index fa4dc077ae0e..1866c27eec69 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -380,7 +380,7 @@ rare; use gpiochip_remove() when it is unavoidable. Most often a gpio_chip is part of an instance-specific structure with state not exposed by the GPIO interfaces, such as addressing, power management, -and more. Chips such as codecs will have complex non-GPIO state, +and more. Chips such as codecs will have complex non-GPIO state. Any debugfs dump method should normally ignore signals which haven't been requested as GPIOs. They can use gpiochip_is_requested(), which returns @@ -531,7 +531,14 @@ and have the following read/write attributes: This file exists only if the pin can be configured as an interrupt generating input pin. -GPIO controllers have paths like /sys/class/gpio/chipchip42/ (for the + "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. |