Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 73 insertions, 0 deletions

diff --git a/Documentation/leds/leds-class-flash.txt b/Documentation/leds/leds-class-flash.txt
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+
+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
+
+
+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.