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The "input" trigger makes the associated GPIO an input. This is to support the Raspberry Pi PWR LED, which is driven by external hardware in normal use. N.B. pwr_led is not available on Model A or B boards. leds-gpio: Implement the brightness_get method The power LED uses some clever logic that means it is driven by a voltage measuring circuit when configured as input, otherwise it is driven by the GPIO output value. This patch wires up the brightness_get method for leds-gpio so that user-space can monitor the LED value via /sys/class/gpio/led1/brightness. Using the input trigger this returns an indication of the system power health, otherwise it is just whatever value the trigger has written most recently. See: https://github.com/raspberrypi/linux/issues/1064
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.