2015-03-05 00:14:24 +08:00
|
|
|
|
|
|
|
|
Flash LED handling under Linux
|
|
|
|
|
==============================
|
|
|
|
|
|
|
|
|
|
Some LED devices provide two modes - torch and flash. In the LED subsystem
|
|
|
|
|
those modes are supported by LED class (see Documentation/leds/leds-class.txt)
|
|
|
|
|
and LED Flash class respectively. The torch mode related features are enabled
|
|
|
|
|
by default and the flash ones only if a driver declares it by setting
|
|
|
|
|
LED_DEV_CAP_FLASH flag.
|
|
|
|
|
|
|
|
|
|
In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
|
|
|
|
|
must be defined in the kernel config. A LED Flash class driver must be
|
|
|
|
|
registered in the LED subsystem with led_classdev_flash_register function.
|
|
|
|
|
|
|
|
|
|
Following sysfs attributes are exposed for controlling flash LED devices:
|
|
|
|
|
(see Documentation/ABI/testing/sysfs-class-led-flash)
|
|
|
|
|
- flash_brightness
|
|
|
|
|
- max_flash_brightness
|
|
|
|
|
- flash_timeout
|
|
|
|
|
- max_flash_timeout
|
|
|
|
|
- flash_strobe
|
|
|
|
|
- flash_fault
|
2015-06-08 17:02:18 +08:00
|
|
|
|
|
|
|
|
|
|
|
|
|
V4L2 flash wrapper for flash LEDs
|
|
|
|
|
=================================
|
|
|
|
|
|
|
|
|
|
A LED subsystem driver can be controlled also from the level of VideoForLinux2
|
|
|
|
|
subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to
|
|
|
|
|
be defined in the kernel config.
|
|
|
|
|
|
|
|
|
|
The driver must call the v4l2_flash_init function to get registered in the
|
|
|
|
|
V4L2 subsystem. The function takes six arguments:
|
|
|
|
|
- dev : flash device, e.g. an I2C device
|
|
|
|
|
- of_node : of_node of the LED, may be NULL if the same as device's
|
|
|
|
|
- fled_cdev : LED flash class device to wrap
|
|
|
|
|
- iled_cdev : LED flash class device representing indicator LED associated with
|
|
|
|
|
fled_cdev, may be NULL
|
|
|
|
|
- ops : V4L2 specific ops
|
|
|
|
|
* external_strobe_set - defines the source of the flash LED strobe -
|
|
|
|
|
V4L2_CID_FLASH_STROBE control or external source, typically
|
|
|
|
|
a sensor, which makes it possible to synchronise the flash
|
|
|
|
|
strobe start with exposure start,
|
|
|
|
|
* intensity_to_led_brightness and led_brightness_to_intensity - perform
|
|
|
|
|
enum led_brightness <-> V4L2 intensity conversion in a device
|
|
|
|
|
specific manner - they can be used for devices with non-linear
|
|
|
|
|
LED current scale.
|
|
|
|
|
- config : configuration for V4L2 Flash sub-device
|
|
|
|
|
* dev_name - the name of the media entity, unique in the system,
|
|
|
|
|
* flash_faults - bitmask of flash faults that the LED flash class
|
|
|
|
|
device can report; corresponding LED_FAULT* bit definitions are
|
|
|
|
|
available in <linux/led-class-flash.h>,
|
|
|
|
|
* torch_intensity - constraints for the LED in TORCH mode
|
|
|
|
|
in microamperes,
|
|
|
|
|
* indicator_intensity - constraints for the indicator LED
|
|
|
|
|
in microamperes,
|
|
|
|
|
* has_external_strobe - determines whether the flash strobe source
|
|
|
|
|
can be switched to external,
|
|
|
|
|
|
|
|
|
|
On remove the v4l2_flash_release function has to be called, which takes one
|
|
|
|
|
argument - struct v4l2_flash pointer returned previously by v4l2_flash_init.
|
|
|
|
|
This function can be safely called with NULL or error pointer argument.
|
|
|
|
|
|
|
|
|
|
Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the
|
|
|
|
|
v4l2 flash wrapper.
|
|
|
|
|
|
|
|
|
|
Once the V4L2 sub-device is registered by the driver which created the Media
|
|
|
|
|
controller device, the sub-device node acts just as a node of a native V4L2
|
|
|
|
|
flash API device would. The calls are simply routed to the LED flash API.
|
|
|
|
|
|
|
|
|
|
Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface
|
|
|
|
|
unavailable. The interface is re-enabled after the V4L2 flash sub-device
|
|
|
|
|
is closed.
|
