diff options
Diffstat (limited to 'Documentation/leds/leds-class-flash.rst')
| -rw-r--r-- | Documentation/leds/leds-class-flash.rst | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/Documentation/leds/leds-class-flash.rst b/Documentation/leds/leds-class-flash.rst new file mode 100644 index 000000000000..6ec12c5a1a0e --- /dev/null +++ b/Documentation/leds/leds-class-flash.rst @@ -0,0 +1,90 @@ +============================== +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.rst) +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. |