drm/radeon: 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

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

1 files changed, 11 insertions, 9 deletions

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
index 3e3290c203c6..b435c859dcbc 100644
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -421,19 +421,21 @@ bool radeon_dp_getdpcd(struct radeon_connector *radeon_connector)
 {
         struct radeon_connector_atom_dig *dig_connector = radeon_connector->con_priv;
         u8 msg[DP_DPCD_SIZE];
-        int ret;
+        int ret, i;
 
-        ret = drm_dp_dpcd_read(&radeon_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(&radeon_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);
 
-                radeon_dp_probe_oui(radeon_connector);
+                        radeon_dp_probe_oui(radeon_connector);
 
-                return true;
+                        return true;
+                }
         }
         dig_connector->dpcd[0] = 0;
         return false;