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90 lines
3.2 KiB
90 lines
3.2 KiB
============================== |
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Flash LED handling under Linux |
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============================== |
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Some LED devices provide two modes - torch and flash. In the LED subsystem |
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those modes are supported by LED class (see Documentation/leds/leds-class.rst) |
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and LED Flash class respectively. The torch mode related features are enabled |
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by default and the flash ones only if a driver declares it by setting |
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LED_DEV_CAP_FLASH flag. |
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In order to enable the support for flash LEDs CONFIG_LEDS_CLASS_FLASH symbol |
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must be defined in the kernel config. A LED Flash class driver must be |
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registered in the LED subsystem with led_classdev_flash_register function. |
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Following sysfs attributes are exposed for controlling flash LED devices: |
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(see Documentation/ABI/testing/sysfs-class-led-flash) |
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- flash_brightness |
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- max_flash_brightness |
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- flash_timeout |
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- max_flash_timeout |
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- flash_strobe |
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- flash_fault |
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V4L2 flash wrapper for flash LEDs |
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================================= |
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A LED subsystem driver can be controlled also from the level of VideoForLinux2 |
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subsystem. In order to enable this CONFIG_V4L2_FLASH_LED_CLASS symbol has to |
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be defined in the kernel config. |
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The driver must call the v4l2_flash_init function to get registered in the |
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V4L2 subsystem. The function takes six arguments: |
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- dev: |
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flash device, e.g. an I2C device |
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- of_node: |
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of_node of the LED, may be NULL if the same as device's |
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- fled_cdev: |
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LED flash class device to wrap |
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- iled_cdev: |
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LED flash class device representing indicator LED associated with |
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fled_cdev, may be NULL |
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- ops: |
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V4L2 specific ops |
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* external_strobe_set |
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defines the source of the flash LED strobe - |
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V4L2_CID_FLASH_STROBE control or external source, typically |
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a sensor, which makes it possible to synchronise the flash |
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strobe start with exposure start, |
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* intensity_to_led_brightness and led_brightness_to_intensity |
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perform |
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enum led_brightness <-> V4L2 intensity conversion in a device |
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specific manner - they can be used for devices with non-linear |
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LED current scale. |
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- config: |
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configuration for V4L2 Flash sub-device |
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* dev_name |
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the name of the media entity, unique in the system, |
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* flash_faults |
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bitmask of flash faults that the LED flash class |
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device can report; corresponding LED_FAULT* bit definitions are |
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available in <linux/led-class-flash.h>, |
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* torch_intensity |
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constraints for the LED in TORCH mode |
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in microamperes, |
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* indicator_intensity |
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constraints for the indicator LED |
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in microamperes, |
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* has_external_strobe |
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determines whether the flash strobe source |
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can be switched to external, |
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On remove the v4l2_flash_release function has to be called, which takes one |
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argument - struct v4l2_flash pointer returned previously by v4l2_flash_init. |
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This function can be safely called with NULL or error pointer argument. |
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Please refer to drivers/leds/leds-max77693.c for an exemplary usage of the |
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v4l2 flash wrapper. |
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Once the V4L2 sub-device is registered by the driver which created the Media |
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controller device, the sub-device node acts just as a node of a native V4L2 |
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flash API device would. The calls are simply routed to the LED flash API. |
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Opening the V4L2 flash sub-device makes the LED subsystem sysfs interface |
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unavailable. The interface is re-enabled after the V4L2 flash sub-device |
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is closed.
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