The documentation being added contains overall description of the Flash Manager functionality and the related sysfs attributes. Signed-off-by: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx> Acked-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> Cc: Bryan Wu <cooloney@xxxxxxxxx> Cc: Richard Purdie <rpurdie@xxxxxxxxx> --- Documentation/leds/leds-class-flash.txt | 64 +++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt index 8a9c17e..417b984 100644 --- a/Documentation/leds/leds-class-flash.txt +++ b/Documentation/leds/leds-class-flash.txt @@ -52,3 +52,67 @@ 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. + + +Flash Manager +============= + +Flash LED devices often provide two ways of strobing the flash: software +(e.g. by setting a bit in a register) and hardware, by asserting dedicated pin, +which is usually connected to a camera sensor device. There are also flash led +devices which support only hardware strobing - in such cases a multiplexer +device is employed to route the flash strobe signal either from the SoC GPIO or +from the external strobe signal provider, e.g. camera sensor. +Use of multiplexers allows also to change the flash-sensor connection +dynamically if there is more than one flash or external strobe signal provider +available on the board. + +In order to address the aforementioned cases the Flash Manager functionality +has been introduced. Flash Manager is a part of the LED Flash Class. +It maintains information about flashes, software and external strobe signal +providers and multiplexers that route strobe signals among them. +Flash Manager becomes available after defining CONFIG_LEDS_FLASH_MANAGER +symbol in the kernel config. + +A flash led device is registered in the Flash Manager only if its Device Tree +node contains information about the topology of strobe signals that can be +routed to the device. The related device node has to be passed int the third +argument to the led_classdev_flash_register function. +The device_node is expected to include one gate-software-strobe subnode and +at least one gate-external-strobeN subnode. Besides that there must defined +a flash_muxes node aggregating all the multiplexers that can be referenced +by the flash led devices. (for mote details see Documentation/devicetree/ +bindings/leds/ leds-flash-manager.txt). + +Flash manager adds following sysfs attributes to the LED Flash Clash +device sysfs interface: + + - strobe_provider - id of the external strobe signal provider associated + with the flash led device. It is created only if + there is more than one external strobe signal + provider defined (RW). + - strobe_providerN - names of the strobe signal providers available + for the flash led device, where N is the + identifier of a strobe signal provider (RO) + + +LED Flash Class multiplexers +============================ + +Multiplexers are an indispensable part of the Flash Manager. Flash Manager has +its own led_flash_gpio_mux* helpers for creating, releasing and operating on +the simple gpio driven multiplexers (the ones whose lines are selected by +changing the state of its selector pins). + +It is however possible that a more advanced device will be used for routing +strobe signals. This kind of devices are known to the Flash Manager as +"asynchronous muxes" and can be registered in arbitrary moment with use of +led_flash_manager_bind_async_mux API and unregistered with +led_flash_manager_unbind_async_mux. (see Documentation/leds/leds-async-mux.c +for the exemplary implementation of the async mux driver). + +If a LED Flash Class device declares dependency on an async mux, then strobing +the flash, or setting external strobe, will succeed only wnen the async mux +has been bound to the Flash Manager. Async mux module, once bound, can be +removed only after all LED Flash Class devices using it are unregistered +from the Flash Manager. -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
