blob: 8da3c6f4b60b8d095056f98a5da495d6d971931e [file] [log] [blame]
Jacek Anaszewskif6ad3952015-03-04 08:14:24 -08001
2Flash LED handling under Linux
3==============================
4
5Some LED devices provide two modes - torch and flash. In the LED subsystem
6those modes are supported by LED class (see Documentation/leds/leds-class.txt)
7and LED Flash class respectively. The torch mode related features are enabled
8by default and the flash ones only if a driver declares it by setting
9LED_DEV_CAP_FLASH flag.
10
11In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol
12must be defined in the kernel config. A LED Flash class driver must be
13registered in the LED subsystem with led_classdev_flash_register function.
14
15Following sysfs attributes are exposed for controlling flash LED devices:
16(see Documentation/ABI/testing/sysfs-class-led-flash)
17 - flash_brightness
18 - max_flash_brightness
19 - flash_timeout
20 - max_flash_timeout
21 - flash_strobe
22 - flash_fault
Jacek Anaszewskiaaf2cbc2015-06-08 02:02:18 -070023
24
25V4L2 flash wrapper for flash LEDs
26=================================
27
28A LED subsystem driver can be controlled also from the level of VideoForLinux2
29subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to
30be defined in the kernel config.
31
32The driver must call the v4l2_flash_init function to get registered in the
33V4L2 subsystem. The function takes six arguments:
34- dev : flash device, e.g. an I2C device
35- of_node : of_node of the LED, may be NULL if the same as device's
36- fled_cdev : LED flash class device to wrap
37- iled_cdev : LED flash class device representing indicator LED associated with
38 fled_cdev, may be NULL
39- ops : V4L2 specific ops
40 * external_strobe_set - defines the source of the flash LED strobe -
41 V4L2_CID_FLASH_STROBE control or external source, typically
42 a sensor, which makes it possible to synchronise the flash
43 strobe start with exposure start,
44 * intensity_to_led_brightness and led_brightness_to_intensity - perform
45 enum led_brightness <-> V4L2 intensity conversion in a device
46 specific manner - they can be used for devices with non-linear
47 LED current scale.
48- config : configuration for V4L2 Flash sub-device
49 * dev_name - the name of the media entity, unique in the system,
50 * flash_faults - bitmask of flash faults that the LED flash class
51 device can report; corresponding LED_FAULT* bit definitions are
52 available in <linux/led-class-flash.h>,
53 * torch_intensity - constraints for the LED in TORCH mode
54 in microamperes,
55 * indicator_intensity - constraints for the indicator LED
56 in microamperes,
57 * has_external_strobe - determines whether the flash strobe source
58 can be switched to external,
59
60On remove the v4l2_flash_release function has to be called, which takes one
61argument - struct v4l2_flash pointer returned previously by v4l2_flash_init.
62This function can be safely called with NULL or error pointer argument.
63
64Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the
65v4l2 flash wrapper.
66
67Once the V4L2 sub-device is registered by the driver which created the Media
68controller device, the sub-device node acts just as a node of a native V4L2
69flash API device would. The calls are simply routed to the LED flash API.
70
71Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface
72unavailable. The interface is re-enabled after the V4L2 flash sub-device
73is closed.