drm/amd: Query and use ACPI backlight caps

ACPI ATIF has a function called query
backlight transfer characteristics.  Among the
information returned by this function is
the minimum and maximum input signals for the
backlight

Call that function on ACPI init.  When DM
backlight device is updated, copy over the
backlight caps into DM, but only once.  Use
the backlight caps in the backlight-to-dc
calculation

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 47 insertions, 12 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 1ed079a6ca81..a5ba1d6990cc 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1589,27 +1589,60 @@ static int amdgpu_dm_mode_config_init(struct amdgpu_device *adev)
 	return 0;
 }
 
+#define AMDGPU_DM_DEFAULT_MIN_BACKLIGHT 12
+#define AMDGPU_DM_DEFAULT_MAX_BACKLIGHT 255
+
 #if defined(CONFIG_BACKLIGHT_CLASS_DEVICE) ||\
 	defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE)
 
+static void amdgpu_dm_update_backlight_caps(struct amdgpu_display_manager *dm)
+{
+#if defined(CONFIG_ACPI)
+	struct amdgpu_dm_backlight_caps caps;
+
+	if (dm->backlight_caps.caps_valid)
+		return;
+
+	amdgpu_acpi_get_backlight_caps(dm->adev, &caps);
+	if (caps.caps_valid) {
+		dm->backlight_caps.min_input_signal = caps.min_input_signal;
+		dm->backlight_caps.max_input_signal = caps.max_input_signal;
+		dm->backlight_caps.caps_valid = true;
+	} else {
+		dm->backlight_caps.min_input_signal =
+				AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
+		dm->backlight_caps.max_input_signal =
+				AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
+	}
+#else
+	dm->backlight_min_input_signal = AMDGPU_DM_DEFAULT_MIN_BACKLIGHT;
+	dm->backlight_max_input_signal = AMDGPU_DM_DEFAULT_MAX_BACKLIGHT;
+#endif
+}
+
 static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
+	struct amdgpu_dm_backlight_caps caps;
+	uint32_t brightness = bd->props.brightness;
 
-	/* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
-	 * and 16 bit fractional, where 1.0 is max backlight value.
-	 * bd->props.brightness is 8 bit format and needs to be converted by
-	 * scaling via copy lower byte to upper byte of 16 bit value.
-	 */
-	uint32_t brightness = bd->props.brightness * 0x101;
-
+	amdgpu_dm_update_backlight_caps(dm);
+	caps = dm->backlight_caps;
 	/*
-	 * PWM interperts 0 as 100% rather than 0% because of HW
-	 * limitation for level 0.  So limiting minimum brightness level
-	 * to 1.
+	 * The brightness input is in the range 0-255
+	 * It needs to be rescaled to be between the
+	 * requested min and max input signal
+	 *
+	 * It also needs to be scaled up by 0x101 to
+	 * match the DC interface which has a range of
+	 * 0 to 0xffff
 	 */
-	if (bd->props.brightness < 1)
-		brightness = 0x101;
+	brightness =
+		brightness
+		* 0x101
+		* (caps.max_input_signal - caps.min_input_signal)
+		/ AMDGPU_MAX_BL_LEVEL
+		+ caps.min_input_signal * 0x101;
 
 	if (dc_link_set_backlight_level(dm->backlight_link,
 			brightness, 0, 0))
@@ -1639,6 +1672,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_display_manager *dm)
 	char bl_name[16];
 	struct backlight_properties props = { 0 };
 
+	amdgpu_dm_update_backlight_caps(dm);
+
 	props.max_brightness = AMDGPU_MAX_BL_LEVEL;
 	props.brightness = AMDGPU_MAX_BL_LEVEL;
 	props.type = BACKLIGHT_RAW;