| Message ID | 20190613194326.180889-5-mka@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | backlight: Expose brightness curve type through sysfs | expand |
On 13/06/2019 20:43, Matthias Kaehlcke wrote: > Check if a brightness curve specified in the device tree is linear or > not and set the corresponding property accordingly. This makes the > scale type available to userspace via the 'scale' sysfs attribute. > > To determine if a curve is linear it is compared to a interpolated linear > curve between min and max brightness. The curve is considered linear if > no value deviates more than +/-5% of ${brightness_range} from their > interpolated value. > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > --- > drivers/video/backlight/pwm_bl.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > index f067fe7aa35d..912407b6d67f 100644 > --- a/drivers/video/backlight/pwm_bl.c > +++ b/drivers/video/backlight/pwm_bl.c > @@ -404,6 +404,26 @@ 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]; > + unsigned int slope = (100 * (max_val - min_val)) / nlevels; Why 100 (rather than a power of 2)? It would also be good to have a comment here saying what the maximum quantization error is. Doesn't have to be over complex just mentioning something like the following (assuming you agree that its true ;-) ): Multiplying by XXX means that even in pathalogical cases such as (max_val - min_val) == nlevels then the error at max_val is less than 1%. With a suitable comment in the fixed point code: Acked-by: Daniel Thompson <daniel.thompson@linaro.org> Daniel. > + 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) / 100); > + 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; > @@ -567,6 +587,11 @@ static int pwm_backlight_probe(struct platform_device *pdev) > > 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 >
Hi Daniel, On Fri, Jun 21, 2019 at 02:10:19PM +0100, Daniel Thompson wrote: > On 13/06/2019 20:43, Matthias Kaehlcke wrote: > > Check if a brightness curve specified in the device tree is linear or > > not and set the corresponding property accordingly. This makes the > > scale type available to userspace via the 'scale' sysfs attribute. > > > > To determine if a curve is linear it is compared to a interpolated linear > > curve between min and max brightness. The curve is considered linear if > > no value deviates more than +/-5% of ${brightness_range} from their > > interpolated value. > > > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org> > > --- > > drivers/video/backlight/pwm_bl.c | 25 +++++++++++++++++++++++++ > > 1 file changed, 25 insertions(+) > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > index f067fe7aa35d..912407b6d67f 100644 > > --- a/drivers/video/backlight/pwm_bl.c > > +++ b/drivers/video/backlight/pwm_bl.c > > @@ -404,6 +404,26 @@ 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]; > > + unsigned int slope = (100 * (max_val - min_val)) / nlevels; > > Why 100 (rather than a power of 2)? I guess it came from the decimal part of my brain, I can change it to 128 ;-) > It would also be good to have a comment here saying what the maximum > quantization error is. Doesn't have to be over complex just mentioning > something like the following (assuming you agree that its true ;-) ): > > Multiplying by XXX means that even in pathalogical cases such as > (max_val - min_val) == nlevels then the error at max_val is less than > 1%. Sounds good, thanks for the suggestion! > With a suitable comment in the fixed point code: > Acked-by: Daniel Thompson <daniel.thompson@linaro.org> Thanks
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index f067fe7aa35d..912407b6d67f 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -404,6 +404,26 @@ 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]; + unsigned int slope = (100 * (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) / 100); + 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; @@ -567,6 +587,11 @@ static int pwm_backlight_probe(struct platform_device *pdev) 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
Check if a brightness curve specified in the device tree is linear or not and set the corresponding property accordingly. This makes the scale type available to userspace via the 'scale' sysfs attribute. To determine if a curve is linear it is compared to a interpolated linear curve between min and max brightness. The curve is considered linear if no value deviates more than +/-5% of ${brightness_range} from their interpolated value. Signed-off-by: Matthias Kaehlcke <mka@chromium.org> --- drivers/video/backlight/pwm_bl.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)