projects / linux-block.git / blame
| Commit | Line | Data |
|---|---|---|
| 8dab9197 | 1 | ============================== |
| f6ad395b JA |
2 | Flash LED handling under Linux |
| 3 | ============================== | |
| 4 | ||
| 5 | Some LED devices provide two modes - torch and flash. In the LED subsystem | |
| 8dab9197 | 6 | those modes are supported by LED class (see Documentation/leds/leds-class.rst) |
| f6ad395b JA |
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) | |
| 8dab9197 | 17 | |
| f6ad395b JA |
18 | - flash_brightness |
| 19 | - max_flash_brightness | |
| 20 | - flash_timeout | |
| 21 | - max_flash_timeout | |
| 22 | - flash_strobe | |
| 23 | - flash_fault | |
| aaf2cbca JA |
24 | |
| 25 | ||
| 26 | V4L2 flash wrapper for flash LEDs | |
| 27 | ================================= | |
| 28 | ||
| 29 | A LED subsystem driver can be controlled also from the level of VideoForLinux2 | |
| 30 | subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to | |
| 31 | be defined in the kernel config. | |
| 32 | ||
| 33 | The driver must call the v4l2_flash_init function to get registered in the | |
| 34 | V4L2 subsystem. The function takes six arguments: | |
| 8dab9197 MCC |
35 | |
| 36 | - dev: | |
| 37 | flash device, e.g. an I2C device | |
| 38 | - of_node: | |
| 39 | of_node of the LED, may be NULL if the same as device's | |
| 40 | - fled_cdev: | |
| 41 | LED flash class device to wrap | |
| 42 | - iled_cdev: | |
| 43 | LED flash class device representing indicator LED associated with | |
| 44 | fled_cdev, may be NULL | |
| 45 | - ops: | |
| 46 | V4L2 specific ops | |
| 47 | ||
| 48 | * external_strobe_set | |
| 49 | defines the source of the flash LED strobe - | |
| aaf2cbca JA |
50 | V4L2_CID_FLASH_STROBE control or external source, typically |
| 51 | a sensor, which makes it possible to synchronise the flash | |
| 52 | strobe start with exposure start, | |
| 8dab9197 MCC |
53 | * intensity_to_led_brightness and led_brightness_to_intensity |
| 54 | perform | |
| aaf2cbca JA |
55 | enum led_brightness <-> V4L2 intensity conversion in a device |
| 56 | specific manner - they can be used for devices with non-linear | |
| 57 | LED current scale. | |
| 8dab9197 MCC |
58 | - config: |
| 59 | configuration for V4L2 Flash sub-device | |
| 60 | ||
| 61 | * dev_name | |
| 62 | the name of the media entity, unique in the system, | |
| 63 | * flash_faults | |
| 64 | bitmask of flash faults that the LED flash class | |
| aaf2cbca JA |
65 | device can report; corresponding LED_FAULT* bit definitions are |
| 66 | available in <linux/led-class-flash.h>, | |
| 8dab9197 MCC |
67 | * torch_intensity |
| 68 | constraints for the LED in TORCH mode | |
| aaf2cbca | 69 | in microamperes, |
| 8dab9197 MCC |
70 | * indicator_intensity |
| 71 | constraints for the indicator LED | |
| aaf2cbca | 72 | in microamperes, |
| 8dab9197 MCC |
73 | * has_external_strobe |
| 74 | determines whether the flash strobe source | |
| aaf2cbca JA |
75 | can be switched to external, |
| 76 | ||
| 77 | On remove the v4l2_flash_release function has to be called, which takes one | |
| 78 | argument - struct v4l2_flash pointer returned previously by v4l2_flash_init. | |
| 79 | This function can be safely called with NULL or error pointer argument. | |
| 80 | ||
| 81 | Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the | |
| 82 | v4l2 flash wrapper. | |
| 83 | ||
| 84 | Once the V4L2 sub-device is registered by the driver which created the Media | |
| 85 | controller device, the sub-device node acts just as a node of a native V4L2 | |
| 86 | flash API device would. The calls are simply routed to the LED flash API. | |
| 87 | ||
| 88 | Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface | |
| 89 | unavailable. The interface is re-enabled after the V4L2 flash sub-device | |
| 90 | is closed. |