drm/radeon: disable ss on DP for DCE3.x

commit d8e24525 upstream.

Seems to cause problems with certain DP monitors.

Bug:
https://bugs.freedesktop.org/show_bug.cgi?id=40699Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: s/radeon_crtc->//]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -956,10 +956,13 @@ static void atombios_crtc_set_pll(struct drm_crtc *crtc, struct drm_display_mode
 						ss_enabled =
 							radeon_atombios_get_ppll_ss_info(rdev, &ss,
 											 ATOM_DP_SS_ID1);
-				} else
+				} else {
 					ss_enabled =
 						radeon_atombios_get_ppll_ss_info(rdev, &ss,
 										 ATOM_DP_SS_ID1);
+				}
+				/* disable spread spectrum on DCE3 DP */
+				ss_enabled = false;
 			}
 			break;
 		case ATOM_ENCODER_MODE_LVDS: