drm/amd/display: Set default brightness according to ACPI

Currently, amdgpu will always set up the brightness at 100% when it
loads.  However this is jarring when the BIOS has it previously
programmed to a much lower value.

The ACPI ATIF method includes two members for "ac_level" and "dc_level".
These represent the default values that should be used if the system is
brought up in AC and DC respectively.

Use these values to set up the default brightness when the backlight
device is registered.

v2: squash in ACPI fix
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -1567,6 +1567,7 @@ static inline int amdgpu_acpi_power_shift_control(struct amdgpu_device *adev,
 						  u8 dev_state, bool drv_state) { return 0; }
 static inline int amdgpu_acpi_smart_shift_update(struct drm_device *dev,
 						 enum amdgpu_ss ss_state) { return 0; }
+static inline void amdgpu_acpi_get_backlight_caps(struct amdgpu_dm_backlight_caps *caps) { }
 #endif
 
 #if defined(CONFIG_ACPI) && defined(CONFIG_SUSPEND)

drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c

@@ -383,6 +383,8 @@ static int amdgpu_atif_query_backlight_caps(struct amdgpu_atif *atif)
 			characteristics.min_input_signal;
 	atif->backlight_caps.max_input_signal =
 			characteristics.max_input_signal;
+	atif->backlight_caps.ac_level = characteristics.ac_level;
+	atif->backlight_caps.dc_level = characteristics.dc_level;
 out:
 	kfree(info);
 	return err;
@@ -1268,6 +1270,8 @@ void amdgpu_acpi_get_backlight_caps(struct amdgpu_dm_backlight_caps *caps)
 	caps->caps_valid = atif->backlight_caps.caps_valid;
 	caps->min_input_signal = atif->backlight_caps.min_input_signal;
 	caps->max_input_signal = atif->backlight_caps.max_input_signal;
+	caps->ac_level = atif->backlight_caps.ac_level;
+	caps->dc_level = atif->backlight_caps.dc_level;
 }
 
 /**

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -77,6 +77,7 @@
 #include <linux/types.h>
 #include <linux/pm_runtime.h>
 #include <linux/pci.h>
+#include <linux/power_supply.h>
 #include <linux/firmware.h>
 #include <linux/component.h>
 #include <linux/dmi.h>
@@ -4571,6 +4572,7 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
 	struct drm_device *drm = aconnector->base.dev;
 	struct amdgpu_display_manager *dm = &drm_to_adev(drm)->dm;
 	struct backlight_properties props = { 0 };
+	struct amdgpu_dm_backlight_caps caps = { 0 };
 	char bl_name[16];
 
 	if (aconnector->bl_idx == -1)
@@ -4583,8 +4585,16 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector)
 		return;
 	}
 
-	props.max_brightness = AMDGPU_MAX_BL_LEVEL;
+	amdgpu_acpi_get_backlight_caps(&caps);
+	if (caps.caps_valid) {
+		if (power_supply_is_system_supplied() > 0)
+			props.brightness = caps.ac_level;
+		else
+			props.brightness = caps.dc_level;
+	} else
 		props.brightness = AMDGPU_MAX_BL_LEVEL;
+
+	props.max_brightness = AMDGPU_MAX_BL_LEVEL;
 	props.type = BACKLIGHT_RAW;
 
 	snprintf(bl_name, sizeof(bl_name), "amdgpu_bl%d",

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -180,6 +180,14 @@ struct amdgpu_dm_backlight_caps {
 	 * @aux_support: Describes if the display supports AUX backlight.
 	 */
 	bool aux_support;
+	/**
+	 * @ac_level: the default brightness if booted on AC
+	 */
+	u8 ac_level;
+	/**
+	 * @dc_level: the default brightness if booted on DC
+	 */
+	u8 dc_level;
 };
 
 /**