diff options
Diffstat (limited to 'drivers/video/backlight/pwm_bl.c')
| -rw-r--r-- | drivers/video/backlight/pwm_bl.c | 72 |
1 files changed, 57 insertions, 15 deletions
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 2201b8c78641..efb4efc2a13d 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -125,8 +125,9 @@ static int pwm_backlight_update_status(struct backlight_device *bl) state.duty_cycle = compute_duty_cycle(pb, brightness); pwm_apply_state(pb->pwm, &state); pwm_backlight_power_on(pb); - } else + } else { pwm_backlight_power_off(pb); + } if (pb->notify_after) pb->notify_after(pb->dev, brightness); @@ -148,15 +149,16 @@ static const struct backlight_ops pwm_backlight_ops = { }; #ifdef CONFIG_OF -#define PWM_LUMINANCE_SCALE 10000 /* luminance scale */ +#define PWM_LUMINANCE_SHIFT 16 +#define PWM_LUMINANCE_SCALE (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */ /* * CIE lightness to PWM conversion. * * The CIE 1931 lightness formula is what actually describes how we perceive * light: - * Y = (L* / 902.3) if L* ≤ 0.08856 - * Y = ((L* + 16) / 116)^3 if L* > 0.08856 + * Y = (L* / 903.3) if L* ≤ 8 + * Y = ((L* + 16) / 116)^3 if L* > 8 * * Where Y is the luminance, the amount of light coming out of the screen, and * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human @@ -165,16 +167,25 @@ static const struct backlight_ops pwm_backlight_ops = { * The following function does the fixed point maths needed to implement the * above formula. */ -static u64 cie1931(unsigned int lightness, unsigned int scale) +static u64 cie1931(unsigned int lightness) { u64 retval; + /* + * @lightness is given as a number between 0 and 1, expressed + * as a fixed-point number in scale + * PWM_LUMINANCE_SCALE. Convert to a percentage, still + * expressed as a fixed-point number, so the above formulas + * can be applied. + */ lightness *= 100; - if (lightness <= (8 * scale)) { - retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023); + if (lightness <= (8 * PWM_LUMINANCE_SCALE)) { + retval = DIV_ROUND_CLOSEST(lightness * 10, 9033); } else { - retval = int_pow((lightness + (16 * scale)) / 116, 3); - retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); + retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116; + retval *= retval * retval; + retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1); + retval >>= 2*PWM_LUMINANCE_SHIFT; } return retval; @@ -208,8 +219,7 @@ int pwm_backlight_brightness_default(struct device *dev, /* Fill the table using the cie1931 algorithm */ for (i = 0; i < data->max_brightness; i++) { retval = cie1931((i * PWM_LUMINANCE_SCALE) / - data->max_brightness, PWM_LUMINANCE_SCALE) * - period; + data->max_brightness) * period; retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE); if (retval > UINT_MAX) return -EINVAL; @@ -387,6 +397,31 @@ int pwm_backlight_brightness_default(struct device *dev, } #endif +static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data) +{ + unsigned int nlevels = data->max_brightness + 1; + unsigned int min_val = data->levels[0]; + unsigned int max_val = data->levels[nlevels - 1]; + /* + * Multiplying by 128 means that even in pathological cases such + * as (max_val - min_val) == nlevels the error at max_val is less + * than 1%. + */ + unsigned int slope = (128 * (max_val - min_val)) / nlevels; + unsigned int margin = (max_val - min_val) / 20; /* 5% */ + int i; + + for (i = 1; i < nlevels; i++) { + unsigned int linear_value = min_val + ((i * slope) / 128); + unsigned int delta = abs(linear_value - data->levels[i]); + + if (delta > margin) + return false; + } + + return true; +} + static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) { struct device_node *node = pb->dev->of_node; @@ -536,18 +571,24 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } + memset(&props, 0, sizeof(struct backlight_properties)); + if (data->levels) { + pb->levels = data->levels; + /* * For the DT case, only when brightness levels is defined * data->levels is filled. For the non-DT case, data->levels * can come from platform data, however is not usual. */ - for (i = 0; i <= data->max_brightness; i++) { + for (i = 0; i <= data->max_brightness; i++) if (data->levels[i] > pb->scale) pb->scale = data->levels[i]; - pb->levels = data->levels; - } + if (pwm_backlight_is_linear(data)) + props.scale = BACKLIGHT_SCALE_LINEAR; + else + props.scale = BACKLIGHT_SCALE_NON_LINEAR; } else if (!data->max_brightness) { /* * If no brightness levels are provided and max_brightness is @@ -574,6 +615,8 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->levels = data->levels; } + + props.scale = BACKLIGHT_SCALE_NON_LINEAR; } else { /* * That only happens for the non-DT case, where platform data @@ -584,7 +627,6 @@ static int pwm_backlight_probe(struct platform_device *pdev) pb->lth_brightness = data->lth_brightness * (state.period / pb->scale); - memset(&props, 0, sizeof(struct backlight_properties)); props.type = BACKLIGHT_RAW; props.max_brightness = data->max_brightness; bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb, |
