drm/radeon: Restore LCD backlight level on resume (>= R5xx)

Instead of only enabling the backlight (which seems to set it to max
brightness), just re-set the current backlight level, which also takes
care of enabling the backlight if necessary.

Only the radeon_atom_encoder_dpms_dig part tested on a Kaveri laptop,
the radeon_atom_encoder_dpms_avivo part is only compile tested.

Cc: stable@vger.kernel.org
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/atombios_encoders.c

@@ -1624,8 +1624,9 @@ radeon_atom_encoder_dpms_avivo(struct drm_encoder *encoder, int mode)
 		} else
 			atom_execute_table(rdev->mode_info.atom_context, index, (uint32_t *)&args);
 		if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT)) {
-			args.ucAction = ATOM_LCD_BLON;
-			atom_execute_table(rdev->mode_info.atom_context, index, (uint32_t *)&args);
+			struct radeon_encoder_atom_dig *dig = radeon_encoder->enc_priv;
+
+			atombios_set_backlight_level(radeon_encoder, dig->backlight_level);
 		}
 		break;
 	case DRM_MODE_DPMS_STANDBY:
@@ -1706,8 +1707,7 @@ radeon_atom_encoder_dpms_dig(struct drm_encoder *encoder, int mode)
 				atombios_dig_encoder_setup(encoder, ATOM_ENCODER_CMD_DP_VIDEO_ON, 0);
 		}
 		if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT))
-			atombios_dig_transmitter_setup(encoder,
-						       ATOM_TRANSMITTER_ACTION_LCD_BLON, 0, 0);
+			atombios_set_backlight_level(radeon_encoder, dig->backlight_level);
 		if (ext_encoder)
 			atombios_external_encoder_setup(encoder, ext_encoder, ATOM_ENABLE);
 		break;