msm: mdss: Optimize backlight mapping calculation for AD

Reduce the rounding error during AD backlight linearization and
attenuation.

Change-Id: Ibf181414512d457d3341bbccf8cf9338aef8ac76
Signed-off-by: Ping Li <pingli@codeaurora.org>

1 files changed, 23 insertions, 16 deletions

diff --git a/drivers/video/fbdev/msm/mdss_mdp_pp.c b/drivers/video/fbdev/msm/mdss_mdp_pp.c
index 444029474157..e79010a6e3fe 100644
--- a/drivers/video/fbdev/msm/mdss_mdp_pp.c
+++ b/drivers/video/fbdev/msm/mdss_mdp_pp.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012-2015, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2012-2016, The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
@@ -5812,11 +5812,17 @@ static int  pp_ad_attenuate_bl(struct mdss_ad_info *ad, u32 bl, u32 *bl_out)
 	u32 shift = 0, ratio_temp = 0;
 	u32 n, lut_interval, bl_att;
 
-	if (bl < 0) {
-		pr_err("Invalid backlight input\n");
+	if (bl < 0 || ad->init.alpha < 0) {
+		pr_err("Invalid input: backlight = %d, alpha = %d\n", bl,
+			ad->init.alpha);
 		return -EINVAL;
 	}
 
+	if (ad->init.alpha == 0) {
+		pr_debug("alpha = %d, hence no attenuation needed\n",
+			ad->init.alpha);
+		return 0;
+	}
 	pr_debug("bl_in = %d\n", bl);
 	/* map panel backlight range to AD backlight range */
 	linear_map(bl, &bl, ad->bl_mfd->panel_info->bl_max,
@@ -5839,12 +5845,9 @@ static int  pp_ad_attenuate_bl(struct mdss_ad_info *ad, u32 bl, u32 *bl_out)
 		lut_interval;
 	pr_debug("n = %u, bl_att_lut[%u] = %u, bl_att_lut[%u] = %u, bl_att = %u\n",
 		n, n, ad->bl_att_lut[n], n + 1, ad->bl_att_lut[n + 1], bl_att);
-	if (ad->init.alpha_base)
-		*bl_out = (ad->init.alpha * bl_att +
-			(ad->init.alpha_base - ad->init.alpha) * bl) /
-			ad->init.alpha_base;
-	else
-		*bl_out = bl;
+	*bl_out = (ad->init.alpha * bl_att +
+		(ad->init.alpha_base - ad->init.alpha) * bl) /
+		ad->init.alpha_base;
 
 	pr_debug("After attenuation = %d\n", *bl_out);
 	/* map AD backlight range back to panel backlight range */
@@ -5860,7 +5863,7 @@ static int pp_ad_linearize_bl(struct mdss_ad_info *ad, u32 bl, u32 *bl_out,
 	int inv)
 {
 
-	u32 n;
+	u32 n, bl_lut_max_index = AD_BL_LIN_LEN - 1;
 	uint32_t *bl_lut = NULL;
 	int ret = -EINVAL;
 
@@ -5885,20 +5888,24 @@ static int pp_ad_linearize_bl(struct mdss_ad_info *ad, u32 bl, u32 *bl_out,
 		MDSS_MDP_AD_BL_SCALE);
 
 	pr_debug("Before linearization = %d\n", bl);
-	n = bl * (AD_BL_LIN_LEN - 1) / MDSS_MDP_AD_BL_SCALE;
+	n = bl * bl_lut_max_index / MDSS_MDP_AD_BL_SCALE;
 	pr_debug("n = %u\n", n);
-	if (n > (AD_BL_LIN_LEN - 1)) {
+	if (n > bl_lut_max_index) {
 		pr_err("Invalid index for BL linearization: %d.\n", n);
 		return ret;
-	} else if (n == (AD_BL_LIN_LEN - 1)) {
+	} else if (n == bl_lut_max_index) {
+		*bl_out = bl_lut[n];
+	} else if (bl == n * MDSS_MDP_AD_BL_SCALE / bl_lut_max_index) {
 		*bl_out = bl_lut[n];
+	} else if (bl == (n + 1) * MDSS_MDP_AD_BL_SCALE / bl_lut_max_index) {
+		*bl_out = bl_lut[n + 1];
 	} else {
 		/* linear piece-wise interpolation */
 		*bl_out = ((bl_lut[n + 1] - bl_lut[n]) *
 			(bl - n * MDSS_MDP_AD_BL_SCALE /
-			(AD_BL_LIN_LEN  - 1)) + bl_lut[n] *
-			MDSS_MDP_AD_BL_SCALE / (AD_BL_LIN_LEN  - 1)) *
-			(AD_BL_LIN_LEN  - 1) / MDSS_MDP_AD_BL_SCALE;
+			bl_lut_max_index) + bl_lut[n] *
+			MDSS_MDP_AD_BL_SCALE / bl_lut_max_index) *
+			bl_lut_max_index / MDSS_MDP_AD_BL_SCALE;
 	}
 	pr_debug("After linearization = %d\n", *bl_out);