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Documentation: leds: Add description of v4l2-flash sub-device

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This patch extends LED Flash class documention by
the description of interactions with v4l2-flash sub-device.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>
This commit is contained in:
Jacek Anaszewski 2015-06-08 02:02:18 -07:00 committed by Bryan Wu
parent 589fca16c1
commit aaf2cbca46
1 changed files with 51 additions and 0 deletions
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Documentation/leds/leds-class-flash.txt
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@ -20,3 +20,54 @@ Following sysfs attributes are exposed for controlling flash LED devices:
- max_flash_timeout
- flash_strobe
- flash_fault
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.