drm/amdgpu: retry dcpd fetch

Retry the dpcd fetch several times.  Some eDP panels
fail several times before the fetch is successful.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=73530

Ported from radeon.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_dp.c b/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
index d54c4b8..9ba0a7d 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
+++ b/drivers/gpu/drm/amd/amdgpu/atombios_dp.c
@@ -358,19 +358,21 @@ int amdgpu_atombios_dp_get_dpcd(struct amdgpu_connector *amdgpu_connector)
 {
        struct amdgpu_connector_atom_dig *dig_connector = amdgpu_connector->con_priv;
        u8 msg[DP_DPCD_SIZE];
-       int ret;
+       int ret, i;
 
-       ret = drm_dp_dpcd_read(&amdgpu_connector->ddc_bus->aux, DP_DPCD_REV, msg,
-                              DP_DPCD_SIZE);
-       if (ret > 0) {
-               memcpy(dig_connector->dpcd, msg, DP_DPCD_SIZE);
+       for (i = 0; i < 7; i++) {
+               ret = drm_dp_dpcd_read(&amdgpu_connector->ddc_bus->aux, DP_DPCD_REV, msg,
+                                      DP_DPCD_SIZE);
+               if (ret == DP_DPCD_SIZE) {
+                       memcpy(dig_connector->dpcd, msg, DP_DPCD_SIZE);
 
-               DRM_DEBUG_KMS("DPCD: %*ph\n", (int)sizeof(dig_connector->dpcd),
-                             dig_connector->dpcd);
+                       DRM_DEBUG_KMS("DPCD: %*ph\n", (int)sizeof(dig_connector->dpcd),
+                                     dig_connector->dpcd);
 
-               amdgpu_atombios_dp_probe_oui(amdgpu_connector);
+                       amdgpu_atombios_dp_probe_oui(amdgpu_connector);
 
-               return 0;
+                       return 0;
+               }
        }
        dig_connector->dpcd[0] = 0;
        return -EINVAL;