drm/radeon/dp: check for errors in dpcd reads

Check to make sure the transaction succeeded before
using the register value.  Fixes occasional link training
problems.

Noticed-by: Sergei Antonov <saproj@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

1 files changed, 25 insertions, 19 deletions

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index bc0119fb6c12..54e4f52549af 100644
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -366,11 +366,11 @@ static void radeon_dp_probe_oui(struct radeon_connector *radeon_connector)
         if (!(dig_connector->dpcd[DP_DOWN_STREAM_PORT_COUNT] & DP_OUI_SUPPORT))
                 return;
 
-        if (drm_dp_dpcd_read(&radeon_connector->ddc_bus->aux, DP_SINK_OUI, buf, 3))
+        if (drm_dp_dpcd_read(&radeon_connector->ddc_bus->aux, DP_SINK_OUI, buf, 3) == 3)
                 DRM_DEBUG_KMS("Sink OUI: %02hx%02hx%02hx\n",
                               buf[0], buf[1], buf[2]);
 
-        if (drm_dp_dpcd_read(&radeon_connector->ddc_bus->aux, DP_BRANCH_OUI, buf, 3))
+        if (drm_dp_dpcd_read(&radeon_connector->ddc_bus->aux, DP_BRANCH_OUI, buf, 3) == 3)
                 DRM_DEBUG_KMS("Branch OUI: %02hx%02hx%02hx\n",
                               buf[0], buf[1], buf[2]);
 }
@@ -419,21 +419,23 @@ int radeon_dp_get_panel_mode(struct drm_encoder *encoder,
 
         if (dp_bridge != ENCODER_OBJECT_ID_NONE) {
                 /* DP bridge chips */
-                drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux,
-                                  DP_EDP_CONFIGURATION_CAP, &tmp);
-                if (tmp & 1)
-                        panel_mode = DP_PANEL_MODE_INTERNAL_DP2_MODE;
-                else if ((dp_bridge == ENCODER_OBJECT_ID_NUTMEG) ||
-                         (dp_bridge == ENCODER_OBJECT_ID_TRAVIS))
-                        panel_mode = DP_PANEL_MODE_INTERNAL_DP1_MODE;
-                else
-                        panel_mode = DP_PANEL_MODE_EXTERNAL_DP_MODE;
+                if (drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux,
+                                      DP_EDP_CONFIGURATION_CAP, &tmp) == 1) {
+                        if (tmp & 1)
+                                panel_mode = DP_PANEL_MODE_INTERNAL_DP2_MODE;
+                        else if ((dp_bridge == ENCODER_OBJECT_ID_NUTMEG) ||
+                                 (dp_bridge == ENCODER_OBJECT_ID_TRAVIS))
+                                panel_mode = DP_PANEL_MODE_INTERNAL_DP1_MODE;
+                        else
+                                panel_mode = DP_PANEL_MODE_EXTERNAL_DP_MODE;
+                }
         } else if (connector->connector_type == DRM_MODE_CONNECTOR_eDP) {
                 /* eDP */
-                drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux,
-                                  DP_EDP_CONFIGURATION_CAP, &tmp);
-                if (tmp & 1)
-                        panel_mode = DP_PANEL_MODE_INTERNAL_DP2_MODE;
+                if (drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux,
+                                      DP_EDP_CONFIGURATION_CAP, &tmp) == 1) {
+                        if (tmp & 1)
+                                panel_mode = DP_PANEL_MODE_INTERNAL_DP2_MODE;
+                }
         }
 
         return panel_mode;
@@ -809,11 +811,15 @@ void radeon_dp_link_train(struct drm_encoder *encoder,
         else
                 dp_info.enc_id |= ATOM_DP_CONFIG_LINK_A;
 
-        drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux, DP_MAX_LANE_COUNT, &tmp);
-        if (ASIC_IS_DCE5(rdev) && (tmp & DP_TPS3_SUPPORTED))
-                dp_info.tp3_supported = true;
-        else
+        if (drm_dp_dpcd_readb(&radeon_connector->ddc_bus->aux, DP_MAX_LANE_COUNT, &tmp)
+            == 1) {
+                if (ASIC_IS_DCE5(rdev) && (tmp & DP_TPS3_SUPPORTED))
+                        dp_info.tp3_supported = true;
+                else
+                        dp_info.tp3_supported = false;
+        } else {
                 dp_info.tp3_supported = false;
+        }
 
         memcpy(dp_info.dpcd, dig_connector->dpcd, DP_RECEIVER_CAP_SIZE);
         dp_info.rdev = rdev;