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-rw-r--r--Documentation/ABI/testing/sysfs-class-backlight26
-rw-r--r--MAINTAINERS1
-rw-r--r--drivers/video/backlight/backlight.c19
-rw-r--r--include/linux/backlight.h8
4 files changed, 54 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight
new file mode 100644
index 000000000000..3ab175a3f5cb
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-backlight
@@ -0,0 +1,26 @@
+What: /sys/class/backlight/<backlight>/scale
+Date: July 2019
+KernelVersion: 5.4
+Contact: Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+ Description of the scale of the brightness curve.
+
+ The human eye senses brightness approximately logarithmically,
+ hence linear changes in brightness are perceived as being
+ non-linear. To achieve a linear perception of brightness changes
+ controls like sliders need to apply a logarithmic mapping for
+ backlights with a linear brightness curve.
+
+ Possible values of the attribute are:
+
+ unknown
+ The scale of the brightness curve is unknown.
+
+ linear
+ The brightness changes linearly with each step. Brightness
+ controls should apply a logarithmic mapping for a linear
+ perception.
+
+ non-linear
+ The brightness changes non-linearly with each step. Brightness
+ controls should use a linear mapping for a linear perception.
diff --git a/MAINTAINERS b/MAINTAINERS
index 5d7bb3024e13..fe75bb96a317 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2907,6 +2907,7 @@ 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 5dc07106a59e..cac3e35d7630 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -32,6 +32,12 @@ static const char *const backlight_types[] = {
[BACKLIGHT_FIRMWARE] = "firmware",
};
+static const char *const backlight_scale_types[] = {
+ [BACKLIGHT_SCALE_UNKNOWN] = "unknown",
+ [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 +252,18 @@ 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 +310,7 @@ 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..c7d6b2e8c3b5 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -46,6 +46,12 @@ enum backlight_notification {
BACKLIGHT_UNREGISTERED,
};
+enum backlight_scale {
+ BACKLIGHT_SCALE_UNKNOWN = 0,
+ BACKLIGHT_SCALE_LINEAR,
+ BACKLIGHT_SCALE_NON_LINEAR,
+};
+
struct backlight_device;
struct fb_info;
@@ -80,6 +86,8 @@ 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 */