| ============================== | |
| 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. |