summaryrefslogtreecommitdiffstats
path: root/drivers/video
diff options
context:
space:
mode:
authorMatthias Kaehlcke <mka@chromium.org>2019-07-09 12:00:05 -0700
committerLee Jones <lee.jones@linaro.org>2019-09-02 15:55:03 +0100
commitd55c028f8b25bdaaba9ae08026052b5b44d031b0 (patch)
tree91c60f22e13ce2ab7eff27f81428e46f52728669 /drivers/video
parent6451e123dec34e295cb0affcd48f671275bdb671 (diff)
downloadlinux-d55c028f8b25bdaaba9ae08026052b5b44d031b0.tar.bz2
backlight: Expose brightness curve type through sysfs
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'. Signed-off-by: Matthias Kaehlcke <mka@chromium.org> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Lee Jones <lee.jones@linaro.org>
Diffstat (limited to 'drivers/video')
-rw-r--r--drivers/video/backlight/backlight.c19
1 files changed, 19 insertions, 0 deletions
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,
};