drm/amdgpu: save/restore backlight level in legacy dce code

Save/restore the backlight level scratch register in S3/S4 so the
backlight level comes back at the previously requested level.

Bug: https://bugzilla.kernel.org/show_bug.cgi?id=199047
Fixes: 4ec6ecf48c64d (drm/amdgpu: drop scratch regs save and restore from S3/S4 handling)
Acked-by: Michel Dänzer <[e-mail]>
Reviewed-by: Harry Wentland <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	u16 firmware_flags;
 	/* pointer to backlight encoder */
 	struct amdgpu_encoder *bl_encoder;
+	u8 bl_level; /* saved backlight level */
 	struct amdgpu_audio	audio; /* audio stuff */
 	int			num_crtc; /* number of crtcs */
 	int			num_hpd; /* number of hpd pins */

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

···
 #include <linux/backlight.h>
 #include "bif/bif_4_1_d.h"
 
-static u8
+u8
 amdgpu_atombios_encoder_get_backlight_level_from_reg(struct amdgpu_device *adev)
 {
 	u8 backlight_level;
···
 	return backlight_level;
 }
 
-static void
+void
 amdgpu_atombios_encoder_set_backlight_level_to_reg(struct amdgpu_device *adev,
 					    u8 backlight_level)
 {

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

···
 #define __ATOMBIOS_ENCODER_H__
 
 u8
+amdgpu_atombios_encoder_get_backlight_level_from_reg(struct amdgpu_device *adev);
+void
+amdgpu_atombios_encoder_set_backlight_level_to_reg(struct amdgpu_device *adev,
+						   u8 backlight_level);
+u8
 amdgpu_atombios_encoder_get_backlight_level(struct amdgpu_encoder *amdgpu_encoder);
 void
 amdgpu_atombios_encoder_set_backlight_level(struct amdgpu_encoder *amdgpu_encoder,

drivers/gpu/drm/amd/amdgpu/dce_v10_0.c

···
 
 static int dce_v10_0_suspend(void *handle)
 {
+	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
+
+	adev->mode_info.bl_level =
+		amdgpu_atombios_encoder_get_backlight_level_from_reg(adev);
+
 	return dce_v10_0_hw_fini(handle);
 }
 
···
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 	int ret;
+
+	amdgpu_atombios_encoder_set_backlight_level_to_reg(adev,
+							   adev->mode_info.bl_level);
 
 	ret = dce_v10_0_hw_init(handle);
 

drivers/gpu/drm/amd/amdgpu/dce_v11_0.c

···
 
 static int dce_v11_0_suspend(void *handle)
 {
+	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
+
+	adev->mode_info.bl_level =
+		amdgpu_atombios_encoder_get_backlight_level_from_reg(adev);
+
 	return dce_v11_0_hw_fini(handle);
 }
 
···
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 	int ret;
+
+	amdgpu_atombios_encoder_set_backlight_level_to_reg(adev,
+							   adev->mode_info.bl_level);
 
 	ret = dce_v11_0_hw_init(handle);
 

drivers/gpu/drm/amd/amdgpu/dce_v6_0.c

···
 
 static int dce_v6_0_suspend(void *handle)
 {
+	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
+
+	adev->mode_info.bl_level =
+		amdgpu_atombios_encoder_get_backlight_level_from_reg(adev);
+
 	return dce_v6_0_hw_fini(handle);
 }
 
···
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 	int ret;
+
+	amdgpu_atombios_encoder_set_backlight_level_to_reg(adev,
+							   adev->mode_info.bl_level);
 
 	ret = dce_v6_0_hw_init(handle);
 

drivers/gpu/drm/amd/amdgpu/dce_v8_0.c

···
 
 static int dce_v8_0_suspend(void *handle)
 {
+	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
+
+	adev->mode_info.bl_level =
+		amdgpu_atombios_encoder_get_backlight_level_from_reg(adev);
+
 	return dce_v8_0_hw_fini(handle);
 }
 
···
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 	int ret;
+
+	amdgpu_atombios_encoder_set_backlight_level_to_reg(adev,
+							   adev->mode_info.bl_level);
 
 	ret = dce_v8_0_hw_init(handle);