drm/amd/display: DispalyPort: Write OUI only if panel supports it

[why]
Organizational Unit Identifier register is optional, and its
presence is published via Down Stream Port Count register.
Writing this register when not available will result in errors

[how]
Read this register and continue writing OUI only if the panel
has the support advertised.

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@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 7cbb1ef..aaa86f0 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
@@ -4227,6 +4227,21 @@ void dp_set_fec_enable(struct dc_link *link, bool enable)
 void dpcd_set_source_specific_data(struct dc_link *link)
 {
        const uint32_t post_oui_delay = 30; // 30ms
+       uint8_t dspc = 0;
+       enum dc_status ret = DC_ERROR_UNEXPECTED;
+
+       ret = core_link_read_dpcd(link, DP_DOWN_STREAM_PORT_COUNT, &dspc,
+                                 sizeof(dspc));
+
+       if (ret != DC_OK) {
+               DC_LOG_ERROR("Error in DP aux read transaction,"
+                            " not writing source specific data\n");
+               return;
+       }
+
+       /* Return if OUI unsupported */
+       if (!(dspc & DP_OUI_SUPPORT))
+               return;
 
        if (!link->dc->vendor_signature.is_valid) {
                struct dpcd_amd_signature amd_signature;