[PATCH] drm/amdgpu: backlight rescaling to original range

[Ikshwaku Chauhan]

[why]
The brightness input is in the range 0-255.It is getting scaled between
the requested min and max input signal and also scaled up by 0x101 to
match the DC interface which has a range of 0 to 0xffff. This scaled
brightness value is not rescaled back to original range(0-255) when
we reads it back.It returns the brightness value in the range of 0-65535
instead of 0-255.

[how]
Rescaled the brightness value form the scaled brightness range 0-65535 to
input brightness range 0-255.

Signed-off-by: Ikshwaku Chauhan <ikshwaku.chauhan at amd.com>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 40 ++++++++++++++-----
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h |  5 +++
 2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 9ab0d8521576..73b0a084e893 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -2881,7 +2881,8 @@ static int set_backlight_via_aux(struct dc_link *link, uint32_t brightness)
 }
 
 static u32 convert_brightness(const struct amdgpu_dm_backlight_caps *caps,
-			      const uint32_t user_brightness)
+			      const uint32_t user_brightness,
+			      enum convert_backlight flag)
 {
 	u32 min, max, conversion_pace;
 	u32 brightness = user_brightness;
@@ -2901,12 +2902,18 @@ static u32 convert_brightness(const struct amdgpu_dm_backlight_caps *caps,
 		 * 0 to 0xffff
 		 */
 		conversion_pace = 0x101;
-		brightness =
-			user_brightness
-			* conversion_pace
-			* (max - min)
-			/ AMDGPU_MAX_BL_LEVEL
-			+ min * conversion_pace;
+		if (flag == set_backlight)
+			brightness =
+				user_brightness
+				* conversion_pace
+				* (max - min)
+				/ AMDGPU_MAX_BL_LEVEL
+				+ min * conversion_pace;
+		else
+			brightness =
+				((user_brightness - min * conversion_pace)
+				 * AMDGPU_MAX_BL_LEVEL)
+				 / (conversion_pace * (max - min));
 	} else {
 		/* TODO
 		 * We are doing a linear interpolation here, which is OK but
@@ -2940,24 +2947,35 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 
 	link = (struct dc_link *)dm->backlight_link;
 
-	brightness = convert_brightness(&caps, bd->props.brightness);
+	brightness = convert_brightness(&caps, bd->props.brightness,
+				set_backlight);
 	// Change brightness based on AUX property
 	if (caps.aux_support)
 		return set_backlight_via_aux(link, brightness);
 
 	rc = dc_link_set_backlight_level(dm->backlight_link, brightness, 0);
-
 	return rc ? 0 : 1;
 }
 
 static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
-	int ret = dc_link_get_backlight_level(dm->backlight_link);
+	struct amdgpu_dm_backlight_caps caps;
+	int ret;
+
+	amdgpu_dm_update_backlight_caps(dm);
+	caps = dm->backlight_caps;
+
+	ret = dc_link_get_backlight_level(dm->backlight_link);
+	ret = (int)convert_brightness(&caps, (uint32_t)ret, get_backlight);
 
 	if (ret == DC_ERROR_UNEXPECTED)
 		return bd->props.brightness;
-	return ret;
+
+	if (ret == AMDGPU_MAX_BL_LEVEL || ret == 0)
+		return ret;
+	else
+		return ret+1;
 }
 
 static const struct backlight_ops amdgpu_dm_backlight_ops = {
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
index 1df0ce047e1c..d54fc00148f9 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
@@ -60,6 +60,11 @@ struct dc;
 struct amdgpu_bo;
 struct dmub_srv;
 
+enum convert_backlight {
+	get_backlight,
+	set_backlight
+};
+
 struct common_irq_params {
 	struct amdgpu_device *adev;
 	enum dc_irq_source irq_src;
-- 
2.17.1