1 files changed, 24 insertions, 15 deletions

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 746eebc411df..efb4efc2a13d 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -125,8 +125,9 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
 		state.duty_cycle = compute_duty_cycle(pb, brightness);
 		pwm_apply_state(pb->pwm, &state);
 		pwm_backlight_power_on(pb);
-	} else
+	} else {
 		pwm_backlight_power_off(pb);
+	}
 
 	if (pb->notify_after)
 		pb->notify_after(pb->dev, brightness);
@@ -148,15 +149,16 @@ static const struct backlight_ops pwm_backlight_ops = {
 };
 
 #ifdef CONFIG_OF
-#define PWM_LUMINANCE_SCALE	10000 /* luminance scale */
+#define PWM_LUMINANCE_SHIFT	16
+#define PWM_LUMINANCE_SCALE	(1 << PWM_LUMINANCE_SHIFT) /* luminance scale */
 
 /*
  * CIE lightness to PWM conversion.
  *
  * The CIE 1931 lightness formula is what actually describes how we perceive
  * light:
- *          Y = (L* / 902.3)           if L* ≤ 0.08856
- *          Y = ((L* + 16) / 116)^3    if L* > 0.08856
+ *          Y = (L* / 903.3)           if L* ≤ 8
+ *          Y = ((L* + 16) / 116)^3    if L* > 8
  *
  * Where Y is the luminance, the amount of light coming out of the screen, and
  * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
@@ -165,16 +167,25 @@ static const struct backlight_ops pwm_backlight_ops = {
  * The following function does the fixed point maths needed to implement the
  * above formula.
  */
-static u64 cie1931(unsigned int lightness, unsigned int scale)
+static u64 cie1931(unsigned int lightness)
 {
 	u64 retval;
 
+	/*
+	 * @lightness is given as a number between 0 and 1, expressed
+	 * as a fixed-point number in scale
+	 * PWM_LUMINANCE_SCALE. Convert to a percentage, still
+	 * expressed as a fixed-point number, so the above formulas
+	 * can be applied.
+	 */
 	lightness *= 100;
-	if (lightness <= (8 * scale)) {
-		retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023);
+	if (lightness <= (8 * PWM_LUMINANCE_SCALE)) {
+		retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
 	} else {
-		retval = int_pow((lightness + (16 * scale)) / 116, 3);
-		retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale));
+		retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116;
+		retval *= retval * retval;
+		retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1);
+		retval >>= 2*PWM_LUMINANCE_SHIFT;
 	}
 
 	return retval;
@@ -208,8 +219,7 @@ int pwm_backlight_brightness_default(struct device *dev,
 	/* Fill the table using the cie1931 algorithm */
 	for (i = 0; i < data->max_brightness; i++) {
 		retval = cie1931((i * PWM_LUMINANCE_SCALE) /
-				 data->max_brightness, PWM_LUMINANCE_SCALE) *
-				 period;
+				 data->max_brightness) * period;
 		retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
 		if (retval > UINT_MAX)
 			return -EINVAL;
@@ -564,18 +574,17 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	memset(&props, 0, sizeof(struct backlight_properties));
 
 	if (data->levels) {
+		pb->levels = data->levels;
+
 		/*
 		 * For the DT case, only when brightness levels is defined
 		 * data->levels is filled. For the non-DT case, data->levels
 		 * can come from platform data, however is not usual.
 		 */
-		for (i = 0; i <= data->max_brightness; i++) {
+		for (i = 0; i <= data->max_brightness; i++)
 			if (data->levels[i] > pb->scale)
 				pb->scale = data->levels[i];
 
-			pb->levels = data->levels;
-		}
-
 		if (pwm_backlight_is_linear(data))
 			props.scale = BACKLIGHT_SCALE_LINEAR;
 		else