drm/amd/display: Retry when read dpcd caps failed.

Some DP panel not detected intermittently due to read dpcd
caps failed when doing hot plug.
[root cause] DC_HPD_CONNECT_INT_DELAY is set to 0, not delay
after HPD toggle and read dpcd data, while some panel need 4ms defer
to read.
[solution] Add a retry when read failed.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index 3b5053570229cdcbb977b6d00674e02fb75b2cd6..b86325bb636f7c10800de4fe64f4e6e040a8792c 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -2278,6 +2278,8 @@ static bool retrieve_link_cap(struct dc_link *link)
        union edp_configuration_cap edp_config_cap;
        union dp_downstream_port_present ds_port = { 0 };
        enum dc_status status = DC_ERROR_UNEXPECTED;
+       uint32_t read_dpcd_retry_cnt = 3;
+       int i;
 
        memset(dpcd_data, '\0', sizeof(dpcd_data));
        memset(&down_strm_port_count,
@@ -2285,11 +2287,15 @@ static bool retrieve_link_cap(struct dc_link *link)
        memset(&edp_config_cap, '\0',
                sizeof(union edp_configuration_cap));
 
-       status = core_link_read_dpcd(
-                       link,
-                       DP_DPCD_REV,
-                       dpcd_data,
-                       sizeof(dpcd_data));
+       for (i = 0; i < read_dpcd_retry_cnt; i++) {
+               status = core_link_read_dpcd(
+                               link,
+                               DP_DPCD_REV,
+                               dpcd_data,
+                               sizeof(dpcd_data));
+               if (status == DC_OK)
+                       break;
+       }
 
        if (status != DC_OK) {
                dm_error("%s: Read dpcd data failed.\n", __func__);