Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 2 Flash LED handling under Linux 3 ============================== 4 5 Some LED devices provide two modes - torch and flash. In the LED subsystem 6 those modes are supported by LED class (see Documentation/leds/leds-class.txt) 7 and LED Flash class respectively. The torch mode related features are enabled 8 by default and the flash ones only if a driver declares it by setting 9 LED_DEV_CAP_FLASH flag. 10 11 In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol 12 must be defined in the kernel config. A LED Flash class driver must be 13 registered in the LED subsystem with led_classdev_flash_register function. 14 15 Following 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 23 24 25 V4L2 flash wrapper for flash LEDs 26 ================================= 27 28 A LED subsystem driver can be controlled also from the level of VideoForLinux2 29 subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to 30 be defined in the kernel config. 31 32 The driver must call the v4l2_flash_init function to get registered in the 33 V4L2 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 60 On remove the v4l2_flash_release function has to be called, which takes one 61 argument - struct v4l2_flash pointer returned previously by v4l2_flash_init. 62 This function can be safely called with NULL or error pointer argument. 63 64 Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the 65 v4l2 flash wrapper. 66 67 Once the V4L2 sub-device is registered by the driver which created the Media 68 controller device, the sub-device node acts just as a node of a native V4L2 69 flash API device would. The calls are simply routed to the LED flash API. 70 71 Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface 72 unavailable. The interface is re-enabled after the V4L2 flash sub-device 73 is closed.