[PATCH 0/4] backlight: Expose brightness curve type through sysfs

[PATCH 0/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

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 is currently opaque
to userspace, so userspace often relies on 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 a new sysfs attribute.

Matthias Kaehlcke (4):
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: Expose brightness curve type through sysfs
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: pwm_bl: Set scale type for brightness curves specified in
    the DT

 .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
 MAINTAINERS                                   |  2 ++
 drivers/video/backlight/backlight.c           | 22 +++++++++++++
 drivers/video/backlight/pwm_bl.c              | 30 ++++++++++++++++-
 include/linux/backlight.h                     | 10 ++++++
 5 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 0/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

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 is currently opaque
to userspace, so userspace often relies on 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 a new sysfs attribute.

Matthias Kaehlcke (4):
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: Expose brightness curve type through sysfs
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: pwm_bl: Set scale type for brightness curves specified in
    the DT

 .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
 MAINTAINERS                                   |  2 ++
 drivers/video/backlight/backlight.c           | 22 +++++++++++++
 drivers/video/backlight/pwm_bl.c              | 30 ++++++++++++++++-
 include/linux/backlight.h                     | 10 ++++++
 5 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Matthias Kaehlcke]

Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
file.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 57f496cff999..d51e74340870 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
 F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
+F:	Documentation/ABI/stable/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Matthias Kaehlcke]

Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
file.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 57f496cff999..d51e74340870 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
 F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
+F:	Documentation/ABI/stable/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

[PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Matthias Kaehlcke]

Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
file.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 57f496cff999..d51e74340870 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
 F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
+F:	Documentation/ABI/stable/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 2/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

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 relies on 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 may be a simple string like
'linear' or 'non-linear', or a composite string similar to
'compatible' strings of the device tree. A composite string consists
of different elements separated by commas, starting with the
most-detailed description and ending with the least-detailed one. An
example for a composite string is "cie-1931,perceptual,non-linear"
This brightness curve was generated with the CIE 1931 algorithm, it
is perceptually linear, but not actually linear in terms of the
emitted light. If userspace doesn't know about 'cie-1931' or
'perceptual' it should at least be able to interpret the 'non-linear'
part.

For devices that don't provide information about the scale of their
brightness curve the value of the 'scale' attribute is 'unknown'.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 drivers/video/backlight/backlight.c           | 22 +++++++++++++
 include/linux/backlight.h                     | 10 ++++++
 4 files changed, 65 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight
new file mode 100644
index 000000000000..924fb68940e6
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-backlight
@@ -0,0 +1,32 @@
+What:		/sys/class/backlight/<backlight>/scale
+Date:		June 2019
+KernelVersion:	5.4
+Contact:	Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+		Description of the scale of the brightness curve. The
+		description consists of one or more elements separated by
+		commas, from the most detailed to the least detailed
+		description.
+
+		Possible values are:
+
+		unknown
+		  The scale of the brightness curve is unknown.
+
+		linear
+		  The brightness changes linearly in terms of the emitted
+		  light, changes are perceived as non-linear by the human eye.
+
+		non-linear
+		  The brightness changes non-linearly in terms of the emitted
+		  light, changes might be perceived as linear by the human eye.
+
+		perceptual,non-linear
+		  The brightness changes non-linearly in terms of the emitted
+		  light, changes should be perceived as linear by the human eye.
+
+		cie-1931,perceptual,non-linear
+		  The brightness curves was calculated with the CIE 1931
+		  algorithm. Brightness changes non-linearly in terms of the
+		  emitted light, changes should be perceived as linear by the
+		  human eye.
diff --git a/MAINTAINERS b/MAINTAINERS
index d51e74340870..c46812510ba5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2858,6 +2858,7 @@ F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
 F:	Documentation/ABI/stable/sysfs-class-backlight
+F:	Documentation/ABI/testing/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 1ef8b6fd62ac..c6e6ea6f2688 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -32,6 +32,15 @@ static const char *const backlight_types[] = {
 	[BACKLIGHT_FIRMWARE] = "firmware",
 };
 
+static const char *const backlight_scale_types[] = {
+	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
+	[BACKLIGHT_SCALE_CIE1931]	= "cie-1931,perceptual,non-linear",
+	[BACKLIGHT_SCALE_PERCEPTUAL]	= "perceptual,non-linear",
+	[BACKLIGHT_SCALE_LINEAR]	= "linear",
+	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
+};
+
+
 #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
 			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
 /* This callback gets called when something important happens inside a
@@ -246,6 +255,18 @@ static ssize_t actual_brightness_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(actual_brightness);
 
+static ssize_t scale_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct backlight_device *bd = to_backlight_device(dev);
+
+	if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR))
+		return sprintf(buf, "unknown\n");
+
+	return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]);
+}
+static DEVICE_ATTR_RO(scale);
+
 static struct class *backlight_class;
 
 #ifdef CONFIG_PM_SLEEP
@@ -292,6 +313,7 @@ static struct attribute *bl_device_attrs[] = {
 	&dev_attr_brightness.attr,
 	&dev_attr_actual_brightness.attr,
 	&dev_attr_max_brightness.attr,
+	&dev_attr_scale.attr,
 	&dev_attr_type.attr,
 	NULL,
 };
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index 0b5897446dca..62e4ab162f34 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -46,6 +46,14 @@ enum backlight_notification {
 	BACKLIGHT_UNREGISTERED,
 };
 
+enum backlight_scale {
+	BACKLIGHT_SCALE_UNKNOWN,
+	BACKLIGHT_SCALE_CIE1931 = 1,
+	BACKLIGHT_SCALE_PERCEPTUAL,
+	BACKLIGHT_SCALE_LINEAR,
+	BACKLIGHT_SCALE_NON_LINEAR,	/* needed for backwards compatibility */
+};
+
 struct backlight_device;
 struct fb_info;
 
@@ -80,6 +88,8 @@ struct backlight_properties {
 	enum backlight_type type;
 	/* Flags used to signal drivers of state changes */
 	unsigned int state;
+	/* Type of the brightness scale (linear, non-linear, ...) */
+	enum backlight_scale scale;
 
 #define BL_CORE_SUSPENDED	(1 << 0)	/* backlight is suspended */
 #define BL_CORE_FBBLANK		(1 << 1)	/* backlight is under an fb blank event */
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 2/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

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 relies on 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 may be a simple string like
'linear' or 'non-linear', or a composite string similar to
'compatible' strings of the device tree. A composite string consists
of different elements separated by commas, starting with the
most-detailed description and ending with the least-detailed one. An
example for a composite string is "cie-1931,perceptual,non-linear"
This brightness curve was generated with the CIE 1931 algorithm, it
is perceptually linear, but not actually linear in terms of the
emitted light. If userspace doesn't know about 'cie-1931' or
'perceptual' it should at least be able to interpret the 'non-linear'
part.

For devices that don't provide information about the scale of their
brightness curve the value of the 'scale' attribute is 'unknown'.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 drivers/video/backlight/backlight.c           | 22 +++++++++++++
 include/linux/backlight.h                     | 10 ++++++
 4 files changed, 65 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight
new file mode 100644
index 000000000000..924fb68940e6
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-backlight
@@ -0,0 +1,32 @@
+What:		/sys/class/backlight/<backlight>/scale
+Date:		June 2019
+KernelVersion:	5.4
+Contact:	Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+		Description of the scale of the brightness curve. The
+		description consists of one or more elements separated by
+		commas, from the most detailed to the least detailed
+		description.
+
+		Possible values are:
+
+		unknown
+		  The scale of the brightness curve is unknown.
+
+		linear
+		  The brightness changes linearly in terms of the emitted
+		  light, changes are perceived as non-linear by the human eye.
+
+		non-linear
+		  The brightness changes non-linearly in terms of the emitted
+		  light, changes might be perceived as linear by the human eye.
+
+		perceptual,non-linear
+		  The brightness changes non-linearly in terms of the emitted
+		  light, changes should be perceived as linear by the human eye.
+
+		cie-1931,perceptual,non-linear
+		  The brightness curves was calculated with the CIE 1931
+		  algorithm. Brightness changes non-linearly in terms of the
+		  emitted light, changes should be perceived as linear by the
+		  human eye.
diff --git a/MAINTAINERS b/MAINTAINERS
index d51e74340870..c46812510ba5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2858,6 +2858,7 @@ F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
 F:	Documentation/ABI/stable/sysfs-class-backlight
+F:	Documentation/ABI/testing/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 1ef8b6fd62ac..c6e6ea6f2688 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -32,6 +32,15 @@ static const char *const backlight_types[] = {
 	[BACKLIGHT_FIRMWARE] = "firmware",
 };
 
+static const char *const backlight_scale_types[] = {
+	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
+	[BACKLIGHT_SCALE_CIE1931]	= "cie-1931,perceptual,non-linear",
+	[BACKLIGHT_SCALE_PERCEPTUAL]	= "perceptual,non-linear",
+	[BACKLIGHT_SCALE_LINEAR]	= "linear",
+	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
+};
+
+
 #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
 			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
 /* This callback gets called when something important happens inside a
@@ -246,6 +255,18 @@ static ssize_t actual_brightness_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(actual_brightness);
 
+static ssize_t scale_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct backlight_device *bd = to_backlight_device(dev);
+
+	if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR))
+		return sprintf(buf, "unknown\n");
+
+	return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]);
+}
+static DEVICE_ATTR_RO(scale);
+
 static struct class *backlight_class;
 
 #ifdef CONFIG_PM_SLEEP
@@ -292,6 +313,7 @@ static struct attribute *bl_device_attrs[] = {
 	&dev_attr_brightness.attr,
 	&dev_attr_actual_brightness.attr,
 	&dev_attr_max_brightness.attr,
+	&dev_attr_scale.attr,
 	&dev_attr_type.attr,
 	NULL,
 };
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index 0b5897446dca..62e4ab162f34 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -46,6 +46,14 @@ enum backlight_notification {
 	BACKLIGHT_UNREGISTERED,
 };
 
+enum backlight_scale {
+	BACKLIGHT_SCALE_UNKNOWN,
+	BACKLIGHT_SCALE_CIE1931 = 1,
+	BACKLIGHT_SCALE_PERCEPTUAL,
+	BACKLIGHT_SCALE_LINEAR,
+	BACKLIGHT_SCALE_NON_LINEAR,	/* needed for backwards compatibility */
+};
+
 struct backlight_device;
 struct fb_info;
 
@@ -80,6 +88,8 @@ struct backlight_properties {
 	enum backlight_type type;
 	/* Flags used to signal drivers of state changes */
 	unsigned int state;
+	/* Type of the brightness scale (linear, non-linear, ...) */
+	enum backlight_scale scale;
 
 #define BL_CORE_SUSPENDED	(1 << 0)	/* backlight is suspended */
 #define BL_CORE_FBBLANK		(1 << 1)	/* backlight is under an fb blank event */
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Matthias Kaehlcke]

For backlight curves calculated with the CIE 1931 algorithm set
the brightness scale type property accordingly. This makes the
scale type available to userspace via the 'scale' sysfs attribute.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 drivers/video/backlight/pwm_bl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index fb45f866b923..f067fe7aa35d 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
+	memset(&props, 0, sizeof(struct backlight_properties));
+
 	if (data->levels) {
 		/*
 		 * For the DT case, only when brightness levels is defined
@@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 			pb->levels = data->levels;
 		}
+
+		props.scale = BACKLIGHT_SCALE_CIE1931;
 	} else {
 		/*
 		 * That only happens for the non-DT case, where platform data
@@ -601,7 +605,6 @@ 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,
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Matthias Kaehlcke]

For backlight curves calculated with the CIE 1931 algorithm set
the brightness scale type property accordingly. This makes the
scale type available to userspace via the 'scale' sysfs attribute.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 drivers/video/backlight/pwm_bl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index fb45f866b923..f067fe7aa35d 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
+	memset(&props, 0, sizeof(struct backlight_properties));
+
 	if (data->levels) {
 		/*
 		 * For the DT case, only when brightness levels is defined
@@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 			pb->levels = data->levels;
 		}
+
+		props.scale = BACKLIGHT_SCALE_CIE1931;
 	} else {
 		/*
 		 * That only happens for the non-DT case, where platform data
@@ -601,7 +605,6 @@ 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,
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

[PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Matthias Kaehlcke]

For backlight curves calculated with the CIE 1931 algorithm set
the brightness scale type property accordingly. This makes the
scale type available to userspace via the 'scale' sysfs attribute.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 drivers/video/backlight/pwm_bl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index fb45f866b923..f067fe7aa35d 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
+	memset(&props, 0, sizeof(struct backlight_properties));
+
 	if (data->levels) {
 		/*
 		 * For the DT case, only when brightness levels is defined
@@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 			pb->levels = data->levels;
 		}
+
+		props.scale = BACKLIGHT_SCALE_CIE1931;
 	} else {
 		/*
 		 * That only happens for the non-DT case, where platform data
@@ -601,7 +605,6 @@ 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,
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Matthias Kaehlcke]

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;
+	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
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

[PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Matthias Kaehlcke]

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;
+	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
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog

Re: [PATCH 2/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

I noticed a few minor things when glancing over the patch on patchwork

On Thu, Jun 13, 2019 at 12:43:24PM -0700, Matthias Kaehlcke wrote:
> 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 relies on more or less reliable

nit: avoid relies ... 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 may be a simple string like
> 'linear' or 'non-linear', or a composite string similar to
> 'compatible' strings of the device tree. A composite string consists
> of different elements separated by commas, starting with the
> most-detailed description and ending with the least-detailed one. An
> example for a composite string is "cie-1931,perceptual,non-linear"
> This brightness curve was generated with the CIE 1931 algorithm, it
> is perceptually linear, but not actually linear in terms of the
> emitted light. If userspace doesn't know about 'cie-1931' or
> 'perceptual' it should at least be able to interpret the 'non-linear'
> part.
> 
> For devices that don't provide information about the scale of their
> brightness curve the value of the 'scale' attribute is 'unknown'.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  drivers/video/backlight/backlight.c           | 22 +++++++++++++
>  include/linux/backlight.h                     | 10 ++++++
>  4 files changed, 65 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-backlight
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight
> new file mode 100644
> index 000000000000..924fb68940e6
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-backlight
> @@ -0,0 +1,32 @@
> +What:		/sys/class/backlight/<backlight>/scale
> +Date:		June 2019
> +KernelVersion:	5.4
> +Contact:	Daniel Thompson <daniel.thompson@linaro.org>
> +Description:
> +		Description of the scale of the brightness curve. The
> +		description consists of one or more elements separated by
> +		commas, from the most detailed to the least detailed
> +		description.
> +
> +		Possible values are:
> +
> +		unknown
> +		  The scale of the brightness curve is unknown.
> +
> +		linear
> +		  The brightness changes linearly in terms of the emitted
> +		  light, changes are perceived as non-linear by the human eye.
> +
> +		non-linear
> +		  The brightness changes non-linearly in terms of the emitted
> +		  light, changes might be perceived as linear by the human eye.
> +
> +		perceptual,non-linear
> +		  The brightness changes non-linearly in terms of the emitted
> +		  light, changes should be perceived as linear by the human eye.
> +
> +		cie-1931,perceptual,non-linear
> +		  The brightness curves was calculated with the CIE 1931

s/curves/curve/

> +static const char *const backlight_scale_types[] = {
> +	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
> +	[BACKLIGHT_SCALE_CIE1931]	= "cie-1931,perceptual,non-linear",
> +	[BACKLIGHT_SCALE_PERCEPTUAL]	= "perceptual,non-linear",
> +	[BACKLIGHT_SCALE_LINEAR]	= "linear",
> +	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
> +};
> +
> +

Delete one blank line

> +enum backlight_scale {
> +	BACKLIGHT_SCALE_UNKNOWN,
> +	BACKLIGHT_SCALE_CIE1931 = 1,
> +	BACKLIGHT_SCALE_PERCEPTUAL,
> +	BACKLIGHT_SCALE_LINEAR,
> +	BACKLIGHT_SCALE_NON_LINEAR,	/* needed for backwards compatibility */

maybe better list the more generic options first, same for the string
table.

Re: [PATCH 2/4] backlight: Expose brightness curve type through sysfs

[Matthias Kaehlcke]

I noticed a few minor things when glancing over the patch on patchwork

On Thu, Jun 13, 2019 at 12:43:24PM -0700, Matthias Kaehlcke wrote:
> 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 relies on more or less reliable

nit: avoid relies ... 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 may be a simple string like
> 'linear' or 'non-linear', or a composite string similar to
> 'compatible' strings of the device tree. A composite string consists
> of different elements separated by commas, starting with the
> most-detailed description and ending with the least-detailed one. An
> example for a composite string is "cie-1931,perceptual,non-linear"
> This brightness curve was generated with the CIE 1931 algorithm, it
> is perceptually linear, but not actually linear in terms of the
> emitted light. If userspace doesn't know about 'cie-1931' or
> 'perceptual' it should at least be able to interpret the 'non-linear'
> part.
> 
> For devices that don't provide information about the scale of their
> brightness curve the value of the 'scale' attribute is 'unknown'.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  .../ABI/testing/sysfs-class-backlight         | 32 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  drivers/video/backlight/backlight.c           | 22 +++++++++++++
>  include/linux/backlight.h                     | 10 ++++++
>  4 files changed, 65 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-backlight
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight
> new file mode 100644
> index 000000000000..924fb68940e6
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-backlight
> @@ -0,0 +1,32 @@
> +What:		/sys/class/backlight/<backlight>/scale
> +Date:		June 2019
> +KernelVersion:	5.4
> +Contact:	Daniel Thompson <daniel.thompson@linaro.org>
> +Description:
> +		Description of the scale of the brightness curve. The
> +		description consists of one or more elements separated by
> +		commas, from the most detailed to the least detailed
> +		description.
> +
> +		Possible values are:
> +
> +		unknown
> +		  The scale of the brightness curve is unknown.
> +
> +		linear
> +		  The brightness changes linearly in terms of the emitted
> +		  light, changes are perceived as non-linear by the human eye.
> +
> +		non-linear
> +		  The brightness changes non-linearly in terms of the emitted
> +		  light, changes might be perceived as linear by the human eye.
> +
> +		perceptual,non-linear
> +		  The brightness changes non-linearly in terms of the emitted
> +		  light, changes should be perceived as linear by the human eye.
> +
> +		cie-1931,perceptual,non-linear
> +		  The brightness curves was calculated with the CIE 1931

s/curves/curve/

> +static const char *const backlight_scale_types[] = {
> +	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
> +	[BACKLIGHT_SCALE_CIE1931]	= "cie-1931,perceptual,non-linear",
> +	[BACKLIGHT_SCALE_PERCEPTUAL]	= "perceptual,non-linear",
> +	[BACKLIGHT_SCALE_LINEAR]	= "linear",
> +	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
> +};
> +
> +

Delete one blank line

> +enum backlight_scale {
> +	BACKLIGHT_SCALE_UNKNOWN,
> +	BACKLIGHT_SCALE_CIE1931 = 1,
> +	BACKLIGHT_SCALE_PERCEPTUAL,
> +	BACKLIGHT_SCALE_LINEAR,
> +	BACKLIGHT_SCALE_NON_LINEAR,	/* needed for backwards compatibility */

maybe better list the more generic options first, same for the string
table.

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Enric Balletbo i Serra]

Hi Matthias,

On 13/6/19 21:43, Matthias Kaehlcke wrote:
> For backlight curves calculated with the CIE 1931 algorithm set
> the brightness scale type property accordingly. This makes the
> scale type available to userspace via the 'scale' sysfs attribute.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Tested on Samsung Chromebook Plus which uses the CIE 1931 algorithm.

Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

> ---
>  drivers/video/backlight/pwm_bl.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index fb45f866b923..f067fe7aa35d 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  		goto err_alloc;
>  	}
>  
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +
>  	if (data->levels) {
>  		/*
>  		 * For the DT case, only when brightness levels is defined
> @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  
>  			pb->levels = data->levels;
>  		}
> +
> +		props.scale = BACKLIGHT_SCALE_CIE1931;
>  	} else {
>  		/*
>  		 * That only happens for the non-DT case, where platform data
> @@ -601,7 +605,6 @@ 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,
> 

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Enric Balletbo i Serra]

Hi Matthias,

On 13/6/19 21:43, Matthias Kaehlcke wrote:
> For backlight curves calculated with the CIE 1931 algorithm set
> the brightness scale type property accordingly. This makes the
> scale type available to userspace via the 'scale' sysfs attribute.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Tested on Samsung Chromebook Plus which uses the CIE 1931 algorithm.

Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

> ---
>  drivers/video/backlight/pwm_bl.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index fb45f866b923..f067fe7aa35d 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  		goto err_alloc;
>  	}
>  
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +
>  	if (data->levels) {
>  		/*
>  		 * For the DT case, only when brightness levels is defined
> @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>  
>  			pb->levels = data->levels;
>  		}
> +
> +		props.scale = BACKLIGHT_SCALE_CIE1931;
>  	} else {
>  		/*
>  		 * That only happens for the non-DT case, where platform data
> @@ -601,7 +605,6 @@ 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,
> 

Re: [PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Daniel Thompson]

On Thu, Jun 13, 2019 at 12:43:23PM -0700, Matthias Kaehlcke wrote:
> Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
> file.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Well spotted. Thanks!

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.

> ---
>  MAINTAINERS | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 57f496cff999..d51e74340870 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
>  F:	include/linux/backlight.h
>  F:	include/linux/pwm_backlight.h
>  F:	Documentation/devicetree/bindings/leds/backlight
> +F:	Documentation/ABI/stable/sysfs-class-backlight
>  
>  BATMAN ADVANCED
>  M:	Marek Lindner <mareklindner@neomailbox.ch>
> -- 
> 2.22.0.rc2.383.gf4fbbf30c2-goog
> 

Re: [PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Daniel Thompson]

On Thu, Jun 13, 2019 at 12:43:23PM -0700, Matthias Kaehlcke wrote:
> Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
> file.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Well spotted. Thanks!

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.

> ---
>  MAINTAINERS | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 57f496cff999..d51e74340870 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
>  F:	include/linux/backlight.h
>  F:	include/linux/pwm_backlight.h
>  F:	Documentation/devicetree/bindings/leds/backlight
> +F:	Documentation/ABI/stable/sysfs-class-backlight
>  
>  BATMAN ADVANCED
>  M:	Marek Lindner <mareklindner@neomailbox.ch>
> -- 
> 2.22.0.rc2.383.gf4fbbf30c2-goog
> 
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Re: [PATCH 1/4] MAINTAINERS: Add entry for stable backlight sysfs ABI documentation

[Daniel Thompson]

On Thu, Jun 13, 2019 at 12:43:23PM -0700, Matthias Kaehlcke wrote:
> Add an entry for the stable backlight sysfs ABI to the MAINTAINERS
> file.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Well spotted. Thanks!

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.

> ---
>  MAINTAINERS | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 57f496cff999..d51e74340870 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2857,6 +2857,7 @@ F:	drivers/video/backlight/
>  F:	include/linux/backlight.h
>  F:	include/linux/pwm_backlight.h
>  F:	Documentation/devicetree/bindings/leds/backlight
> +F:	Documentation/ABI/stable/sysfs-class-backlight
>  
>  BATMAN ADVANCED
>  M:	Marek Lindner <mareklindner@neomailbox.ch>
> -- 
> 2.22.0.rc2.383.gf4fbbf30c2-goog
> 

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Daniel Thompson]

On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> For backlight curves calculated with the CIE 1931 algorithm set
> the brightness scale type property accordingly. This makes the
> scale type available to userspace via the 'scale' sysfs attribute.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

I'd like to keep discussion on patch 2 open a bit longer (it's not part 
of the thread below patch 2 but Pavel had concerns about the sysfs 
interface) so this ack won't really push things forward but FWIW:

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


> ---
>   drivers/video/backlight/pwm_bl.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index fb45f866b923..f067fe7aa35d 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>   		goto err_alloc;
>   	}
>   
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +
>   	if (data->levels) {
>   		/*
>   		 * For the DT case, only when brightness levels is defined
> @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>   
>   			pb->levels = data->levels;
>   		}
> +
> +		props.scale = BACKLIGHT_SCALE_CIE1931;
>   	} else {
>   		/*
>   		 * That only happens for the non-DT case, where platform data
> @@ -601,7 +605,6 @@ 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,
> 

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Daniel Thompson]

On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> For backlight curves calculated with the CIE 1931 algorithm set
> the brightness scale type property accordingly. This makes the
> scale type available to userspace via the 'scale' sysfs attribute.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

I'd like to keep discussion on patch 2 open a bit longer (it's not part 
of the thread below patch 2 but Pavel had concerns about the sysfs 
interface) so this ack won't really push things forward but FWIW:

Acked-by: Daniel Thompson <daniel.thompson@linaro.org>


> ---
>   drivers/video/backlight/pwm_bl.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> index fb45f866b923..f067fe7aa35d 100644
> --- a/drivers/video/backlight/pwm_bl.c
> +++ b/drivers/video/backlight/pwm_bl.c
> @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>   		goto err_alloc;
>   	}
>   
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +
>   	if (data->levels) {
>   		/*
>   		 * For the DT case, only when brightness levels is defined
> @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>   
>   			pb->levels = data->levels;
>   		}
> +
> +		props.scale = BACKLIGHT_SCALE_CIE1931;
>   	} else {
>   		/*
>   		 * That only happens for the non-DT case, where platform data
> @@ -601,7 +605,6 @@ 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,
> 

Re: [PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Daniel Thompson]

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
> 

Re: [PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Daniel Thompson]

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
> 

Re: [PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Matthias Kaehlcke]

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

Re: [PATCH 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

[Matthias Kaehlcke]

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

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Lee Jones]

On Fri, 21 Jun 2019, Daniel Thompson wrote:

> On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > For backlight curves calculated with the CIE 1931 algorithm set
> > the brightness scale type property accordingly. This makes the
> > scale type available to userspace via the 'scale' sysfs attribute.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> the thread below patch 2 but Pavel had concerns about the sysfs interface)
> so this ack won't really push things forward but FWIW:
> 
> Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

Does this depend on patch 2, or is it orthogonal?

> > ---
> >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > index fb45f866b923..f067fe7aa35d 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   		goto err_alloc;
> >   	}
> > +	memset(&props, 0, sizeof(struct backlight_properties));
> > +
> >   	if (data->levels) {
> >   		/*
> >   		 * For the DT case, only when brightness levels is defined
> > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   			pb->levels = data->levels;
> >   		}
> > +
> > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> >   	} else {
> >   		/*
> >   		 * That only happens for the non-DT case, where platform data
> > @@ -601,7 +605,6 @@ 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,
> > 
> 

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Lee Jones]

On Fri, 21 Jun 2019, Daniel Thompson wrote:

> On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > For backlight curves calculated with the CIE 1931 algorithm set
> > the brightness scale type property accordingly. This makes the
> > scale type available to userspace via the 'scale' sysfs attribute.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> the thread below patch 2 but Pavel had concerns about the sysfs interface)
> so this ack won't really push things forward but FWIW:
> 
> Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

Does this depend on patch 2, or is it orthogonal?

> > ---
> >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > index fb45f866b923..f067fe7aa35d 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   		goto err_alloc;
> >   	}
> > +	memset(&props, 0, sizeof(struct backlight_properties));
> > +
> >   	if (data->levels) {
> >   		/*
> >   		 * For the DT case, only when brightness levels is defined
> > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   			pb->levels = data->levels;
> >   		}
> > +
> > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> >   	} else {
> >   		/*
> >   		 * That only happens for the non-DT case, where platform data
> > @@ -601,7 +605,6 @@ 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,
> > 
> 

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Lee Jones]

On Fri, 21 Jun 2019, Daniel Thompson wrote:

> On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > For backlight curves calculated with the CIE 1931 algorithm set
> > the brightness scale type property accordingly. This makes the
> > scale type available to userspace via the 'scale' sysfs attribute.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> the thread below patch 2 but Pavel had concerns about the sysfs interface)
> so this ack won't really push things forward but FWIW:
> 
> Acked-by: Daniel Thompson <daniel.thompson@linaro.org>

Does this depend on patch 2, or is it orthogonal?

> > ---
> >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > index fb45f866b923..f067fe7aa35d 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   		goto err_alloc;
> >   	}
> > +	memset(&props, 0, sizeof(struct backlight_properties));
> > +
> >   	if (data->levels) {
> >   		/*
> >   		 * For the DT case, only when brightness levels is defined
> > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >   			pb->levels = data->levels;
> >   		}
> > +
> > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> >   	} else {
> >   		/*
> >   		 * That only happens for the non-DT case, where platform data
> > @@ -601,7 +605,6 @@ 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,
> > 
> 

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Daniel Thompson]

On Thu, Jun 27, 2019 at 10:24:53AM +0100, Lee Jones wrote:
> On Fri, 21 Jun 2019, Daniel Thompson wrote:
> 
> > On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > > For backlight curves calculated with the CIE 1931 algorithm set
> > > the brightness scale type property accordingly. This makes the
> > > scale type available to userspace via the 'scale' sysfs attribute.
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > 
> > I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> > the thread below patch 2 but Pavel had concerns about the sysfs interface)
> > so this ack won't really push things forward but FWIW:
> > 
> > Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
> 
> Does this depend on patch 2, or is it orthogonal?

IIRC it depends on patch 2 (since that't what introduces props.scale ).


Daniel.

> 
> > > ---
> > >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > > index fb45f866b923..f067fe7aa35d 100644
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   		goto err_alloc;
> > >   	}
> > > +	memset(&props, 0, sizeof(struct backlight_properties));
> > > +
> > >   	if (data->levels) {
> > >   		/*
> > >   		 * For the DT case, only when brightness levels is defined
> > > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   			pb->levels = data->levels;
> > >   		}
> > > +
> > > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> > >   	} else {
> > >   		/*
> > >   		 * That only happens for the non-DT case, where platform data
> > > @@ -601,7 +605,6 @@ 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,
> > > 
> > 
> 
> -- 
> Lee Jones [李琼斯]
> Linaro Services Technical Lead
> Linaro.org │ Open source software for ARM SoCs
> Follow Linaro: Facebook | Twitter | Blog

Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Daniel Thompson]

On Thu, Jun 27, 2019 at 10:24:53AM +0100, Lee Jones wrote:
> On Fri, 21 Jun 2019, Daniel Thompson wrote:
> 
> > On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > > For backlight curves calculated with the CIE 1931 algorithm set
> > > the brightness scale type property accordingly. This makes the
> > > scale type available to userspace via the 'scale' sysfs attribute.
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > 
> > I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> > the thread below patch 2 but Pavel had concerns about the sysfs interface)
> > so this ack won't really push things forward but FWIW:
> > 
> > Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
> 
> Does this depend on patch 2, or is it orthogonal?

IIRC it depends on patch 2 (since that't what introduces props.scale ).


Daniel.

> 
> > > ---
> > >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > > index fb45f866b923..f067fe7aa35d 100644
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   		goto err_alloc;
> > >   	}
> > > +	memset(&props, 0, sizeof(struct backlight_properties));
> > > +
> > >   	if (data->levels) {
> > >   		/*
> > >   		 * For the DT case, only when brightness levels is defined
> > > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   			pb->levels = data->levels;
> > >   		}
> > > +
> > > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> > >   	} else {
> > >   		/*
> > >   		 * That only happens for the non-DT case, where platform data
> > > @@ -601,7 +605,6 @@ 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,
> > > 
> > 
> 
> -- 
> Lee Jones [李琼斯]
> Linaro Services Technical Lead
> Linaro.org │ Open source software for ARM SoCs
> Follow Linaro: Facebook | Twitter | Blog
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Re: [PATCH 3/4] backlight: pwm_bl: Set scale type for CIE 1931 curves

[Daniel Thompson]

On Thu, Jun 27, 2019 at 10:24:53AM +0100, Lee Jones wrote:
> On Fri, 21 Jun 2019, Daniel Thompson wrote:
> 
> > On 13/06/2019 20:43, Matthias Kaehlcke wrote:
> > > For backlight curves calculated with the CIE 1931 algorithm set
> > > the brightness scale type property accordingly. This makes the
> > > scale type available to userspace via the 'scale' sysfs attribute.
> > > 
> > > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > 
> > I'd like to keep discussion on patch 2 open a bit longer (it's not part of
> > the thread below patch 2 but Pavel had concerns about the sysfs interface)
> > so this ack won't really push things forward but FWIW:
> > 
> > Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
> 
> Does this depend on patch 2, or is it orthogonal?

IIRC it depends on patch 2 (since that't what introduces props.scale ).


Daniel.

> 
> > > ---
> > >   drivers/video/backlight/pwm_bl.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > > index fb45f866b923..f067fe7aa35d 100644
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -553,6 +553,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   		goto err_alloc;
> > >   	}
> > > +	memset(&props, 0, sizeof(struct backlight_properties));
> > > +
> > >   	if (data->levels) {
> > >   		/*
> > >   		 * For the DT case, only when brightness levels is defined
> > > @@ -591,6 +593,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> > >   			pb->levels = data->levels;
> > >   		}
> > > +
> > > +		props.scale = BACKLIGHT_SCALE_CIE1931;
> > >   	} else {
> > >   		/*
> > >   		 * That only happens for the non-DT case, where platform data
> > > @@ -601,7 +605,6 @@ 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,
> > > 
> > 
> 
> -- 
> Lee Jones [李琼斯]
> Linaro Services Technical Lead
> Linaro.org │ Open source software for ARM SoCs
> Follow Linaro: Facebook | Twitter | Blog