path: root/Documentation/leds
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authorJacek Anaszewski <>2015-06-08 02:02:18 -0700
committerBryan Wu <>2015-06-10 13:46:28 -0700
commitaaf2cbca46a569b1ec4c292b03fbe2a0a1217e2f (patch)
treeda4b2213e804b66ae83c64da027c7516094fa0b3 /Documentation/leds
parent589fca16c14adec7ebeb601e22850826e18b8f8d (diff)
Documentation: leds: Add description of v4l2-flash sub-device
This patch extends LED Flash class documention by the description of interactions with v4l2-flash sub-device. Signed-off-by: Jacek Anaszewski <> Acked-by: Kyungmin Park <> Cc: Richard Purdie <> Acked-by: Sakari Ailus <> Signed-off-by: Bryan Wu <>
Diffstat (limited to 'Documentation/leds')
1 files changed, 51 insertions, 0 deletions
diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
index 19bb67355424..8da3c6f4b60b 100644
--- a/Documentation/leds/leds-class-flash.txt
+++ b/Documentation/leds/leds-class-flash.txt
@@ -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.