[PATCH] backlight: provide sysfs percent brightness attribute

[H Hartley Sweeten]

It's usually more convenient to set the backlight brightness
as a 'percent' of total brightness rather than using the raw
'brightness' value.

This provides the necessary sysfs attributes to handle this.

Signed-off-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
Cc: Richard Purdie <rpurdie@xxxxxxxxx>

---

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 18829cf..af25bfa 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -190,6 +190,50 @@ static ssize_t backlight_show_actual_brightness(struct device *dev,
 	return rc;
 }
 
+static ssize_t backlight_show_percent(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct backlight_device *bd = to_backlight_device(dev);
+	int percent;
+
+	percent = bd->props.brightness * 100 / bd->props.max_brightness;
+	return sprintf(buf, "%d\n", percent);
+}
+
+static ssize_t backlight_store_percent(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct backlight_device *bd = to_backlight_device(dev);
+	unsigned long percent, brightness;
+	int rc;
+
+	rc = strict_strtoul(buf, 0, &percent);
+	if (rc)
+		return rc;
+
+	brightness = percent * bd->props.max_brightness / 100;
+
+	rc = -ENXIO;
+
+	mutex_lock(&bd->ops_lock);
+	if (bd->ops) {
+		if (brightness > bd->props.max_brightness)
+			rc = -EINVAL;
+		else {
+			pr_debug("backlight: set to %lu%% (brightness of %lu)\n",
+				 percent, brightness);
+			bd->props.brightness = brightness;
+			backlight_update_status(bd);
+			rc = count;
+		}
+	}
+	mutex_unlock(&bd->ops_lock);
+
+	backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
+
+	return rc;
+}
+
 static struct class *backlight_class;
 
 static int backlight_suspend(struct device *dev, pm_message_t state)
@@ -233,6 +277,7 @@ static struct device_attribute bl_device_attributes[] = {
 	__ATTR(actual_brightness, 0444, backlight_show_actual_brightness,
 		     NULL),
 	__ATTR(max_brightness, 0444, backlight_show_max_brightness, NULL),
+	__ATTR(percent, 0644, backlight_show_percent, backlight_store_percent),
 	__ATTR_NULL,
 };
 
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