Backlight brightness curves can have different shapes. The two main types are linear and non-linear curves. The human eye doesn't perceive linearly increasing/decreasing brightness as linear (see also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED linearly to human eye"), hence many backlights use non-linear (often logarithmic) brightness curves. The type of curve currently is opaque to userspace, so userspace often uses more or less reliable heuristics (like the number of brightness levels) to decide whether to treat a backlight device as linear or non-linear. Export the type of the brightness curve via the new sysfs attribute 'scale'. The value of the attribute can be 'linear', 'non-linear' or 'unknown'. For devices that don't provide information about the scale of their brightness curve the value of the 'scale' attribute is 'unknown'.
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| @@ -46,6 +46,12 @@ enum backlight_notification { · 45 unmodified lines | |||
| 46 | BACKLIGHT_UNREGISTERED, | 46 | BACKLIGHT_UNREGISTERED, |
| 47 | }; | 47 | }; |
| 48 | 48 | ||
| 49 | enum backlight_scale { | ||
| 50 | BACKLIGHT_SCALE_UNKNOWN = 0, | ||
| 51 | BACKLIGHT_SCALE_LINEAR, | ||
| 52 | BACKLIGHT_SCALE_NON_LINEAR, | ||
| 53 | }; | ||
| 54 | |||
| 49 | struct backlight_device; | 55 | struct backlight_device; |
| 50 | struct fb_info; | 56 | struct fb_info; |
| 51 | 57 | ||
| @@ -80,6 +86,8 @@ struct backlight_properties { · 28 unmodified lines | |||
| 80 | enum backlight_type type; | 86 | enum backlight_type type; |
| 81 | /* Flags used to signal drivers of state changes */ | 87 | /* Flags used to signal drivers of state changes */ |
| 82 | unsigned int state; | 88 | unsigned int state; |
| 89 | /* Type of the brightness scale (linear, non-linear, ...) */ | ||
| 90 | enum backlight_scale scale; | ||
| 83 | 91 | ||
| 84 | #define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */ | 92 | #define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */ |
| 85 | #define BL_CORE_FBBLANK (1 << 1) /* backlight is under an fb blank event */ | 93 | #define BL_CORE_FBBLANK (1 << 1) /* backlight is under an fb blank event */ |