@@ -8,6 +8,58 @@ LED is defined in max_brightness file. The brightness file will set the brightne
of the LED (taking a value 0-max_brightness). Most LEDs don't have hardware
brightness support so will just be turned on for non-zero brightness settings.
+Some LED devices support two modes - torch and flash. In order to enable
+support for flash LEDs the CONFIG_LEDS_CLASS_FLASH symbol must be defined
+in the kernel config. A flash LED driver must initialize the "flash" field
+of the led_classdev structure (see <linux/leds_flash.h>) to enable flash
+related features of the LED subsystem for the driver.
+
+There are seven sysfs attributes dedicated specifically to the flash LED devices:
+
+ - flash_brightness - flash LED brightness in milliampers (RW)
+ - max_flash_brightness - maximum available flash LED brightness (RO)
+ - flash_timeout - flash strobe duration in milliseconds (RW)
+ - max_flash_timeout - maximum available flash strobe duration (RO)
+ - flash_strobe - flash strobe state (RW)
+ - flash_fault - bitmask of flash faults that may have occured, possible
+ flags are:
+ * 0x01 - flash controller voltage to the flash LED has exceeded
+ the limit specific to the flash controller
+ * 0x02 - the flash strobe was still on when the timeout set by
+ the user has expired; not all flash controllers may set
+ this in all such conditions
+ * 0x04 - the flash controller has overheated
+ * 0x08 - the short circuit protection of the flash controller
+ has been triggered
+ * 0x10 - current in the LED power supply has exceeded the limit
+ specific to the flash controller
+ * 0x40 - flash controller voltage to the flash LED has been below
+ the minimum limit specific to the flash
+ * 0x80 - the input voltage of the flash controller is below
+ the limit under which strobing the flash at full current
+ will not be possible. The condition persists until this
+ flag is no longer set
+ * 0x100 - the temperature of the LED has exceeded its allowed
+ upper limit
+ - hw_triggered - some devices expose dedicated hardware pins for
+ triggering a flash LED - the attribute allows to set
+ this mode (RW)
+
+The LED subsystem driver can be controlled also from the level of
+the VideoForLinux2 subsystem. In order to enable this the CONFIG_V4L2_FLASH
+symbol has to be defined in the kernel config. The driver must
+initialize v4l2_flash_ctrl_config structure and pass it to the v4l2_flash_init
+function. On remove v4l2_flash_release has to be called (see <media/v4l2-flash.h>).
+After proper initialization V4L2 Flash sub-device is created. The sub-device
+must be registered by a V4L2 video device to become available for the user
+space. This is accomplished with use of asynchronous sub-device registration
+mechanism (see <media/v4l2-async.h>).
+A V4l2 Flash sub-device exposes a number of V4L2 controls.
+When the V4L2_CID_FLASH_LED_MODE control is set to V4L2_FLASH_LED_MODE_TORCH
+or V4L2_FLASH_LED_MODE_FLASH the LED subsystem sysfs interface becomes
+unavailable. The interface can be unlocked by setting the mode back
+to V4L2_FLASH_LED_MODE_NONE.
+
The class also introduces the optional concept of an LED trigger. A trigger
is a kernel based source of led events. Triggers can either be simple or
complex. A simple trigger isn't configurable and is designed to slot into