From 808da1bce0ba9121b3b573fc2f25917179276cec Mon Sep 17 00:00:00 2001
From: CTCaer <ctcaer@gmail.com>
Date: Fri, 15 Oct 2021 16:16:24 +0300
Subject: [PATCH] bdk: di: adjust OLED panel brightness curve

The Samsung AMOLED panel least legible backlight is at a high duty (45 / 255).
Change the linear curve to a more appropriate one.
---
 bdk/display/di.c | 4 ++++
 bdk/display/di.h | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/bdk/display/di.c b/bdk/display/di.c
index b19a5db..9396e99 100644
--- a/bdk/display/di.c
+++ b/bdk/display/di.c
@@ -557,6 +557,10 @@ void display_backlight(bool enable)
 
 void display_dsi_backlight_brightness(u32 brightness)
 {
+	// Normalize brightness value by 82% and a base of 45 duty.
+	if (brightness)
+		brightness = (brightness * PANEL_OLED_BL_COEFF / 100) + PANEL_OLED_BL_OFFSET;
+
 	u16 bl_ctrl = byte_swap_16((u16)(brightness * 8));
 	display_dsi_vblank_write(MIPI_DCS_SET_BRIGHTNESS, 2, &bl_ctrl);
 }
diff --git a/bdk/display/di.h b/bdk/display/di.h
index 4f75211..1e0f991 100644
--- a/bdk/display/di.h
+++ b/bdk/display/di.h
@@ -652,6 +652,9 @@
 #define DCS_CONTROL_DISPLAY_DIMMING_CTRL    BIT(3)
 #define DCS_CONTROL_DISPLAY_BRIGHTNESS_CTRL BIT(5)
 
+#define PANEL_OLED_BL_COEFF  82 // 82%.
+#define PANEL_OLED_BL_OFFSET 45 // Least legible backlight duty.
+
 /* Switch Panels:
  *
  * 6.2" panels for Icosa and Iowa skus: