drm/dp: WARN about invalid/unknown link rates and bw codes

Falling back to the lowest value is likely the only thing we can do, but
doing it silently seems like a bad thing to do. Catch it early and make
loud noises.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: NThierry Reding <treding@nvidia.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: NManasi Navare <manasi.d.navare@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171009092959.29021-1-jani.nikula@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -137,8 +137,10 @@ EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
 u8 drm_dp_link_rate_to_bw_code(int link_rate)
 {
 	switch (link_rate) {
-	case 162000:
 	default:
+		WARN(1, "unknown DP link rate %d, using %x\n", link_rate,
+		     DP_LINK_BW_1_62);
+	case 162000:
 		return DP_LINK_BW_1_62;
 	case 270000:
 		return DP_LINK_BW_2_7;
@@ -151,8 +153,9 @@ EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code);
 int drm_dp_bw_code_to_link_rate(u8 link_bw)
 {
 	switch (link_bw) {
-	case DP_LINK_BW_1_62:
 	default:
+		WARN(1, "unknown DP link BW code %x, using 162000\n", link_bw);
+	case DP_LINK_BW_1_62:
 		return 162000;
 	case DP_LINK_BW_2_7:
 		return 270000;