drm/radeon: fix dpms on/off on trinity/aruba v2

The external encoder need to be setup again before enabling the
transmiter. This seems to be only needed on some trinity/aruba
to fix dpms on.

v2: Add comment, only setup again on dce6 ie aruba or newer.

Cc: <stable@kernel.org>
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/atombios_encoders.c

@@ -1392,10 +1392,18 @@ radeon_atom_encoder_dpms_dig(struct drm_encoder *encoder, int mode)
 	case DRM_MODE_DPMS_ON:
 		/* some early dce3.2 boards have a bug in their transmitter control table */
 		if ((rdev->family == CHIP_RV710) || (rdev->family == CHIP_RV730) ||
-		    ASIC_IS_DCE41(rdev) || ASIC_IS_DCE5(rdev))
+		    ASIC_IS_DCE41(rdev) || ASIC_IS_DCE5(rdev)) {
+			if (ASIC_IS_DCE6(rdev)) {
+				/* It seems we need to call ATOM_ENCODER_CMD_SETUP again
+				 * before reenabling encoder on DPMS ON, otherwise we never
+				 * get picture
+				 */
+				atombios_dig_encoder_setup(encoder, ATOM_ENCODER_CMD_SETUP, 0);
+			}
 			atombios_dig_transmitter_setup(encoder, ATOM_TRANSMITTER_ACTION_ENABLE, 0, 0);
-		else
+		} else {
 			atombios_dig_transmitter_setup(encoder, ATOM_TRANSMITTER_ACTION_ENABLE_OUTPUT, 0, 0);
+		}
 		if (ENCODER_MODE_IS_DP(atombios_get_encoder_mode(encoder)) && connector) {
 			if (connector->connector_type == DRM_MODE_CONNECTOR_eDP) {
 				atombios_set_edp_panel_power(connector,