Atm it's assumed that all Synaptics MST branch devices support DSC, which is not exposed via a DP-to-DP peer device, rather a control flag in the branch device's UFP DPCD applying to all the streams going through it. This isn't true for all adapters with this branch device though (for instance the Cakitte USBC->2xHDMI adapter reported in the Closes link below doesn't support DSC). Fix the above by advertising the DSC decompression support only if the capability flag for this in the UFP DPCD is actually set. Cc: Lyude Paul <lyude@xxxxxxxxxx> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12047 Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> --- drivers/gpu/drm/display/drm_dp_mst_topology.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index a040d7dfced17..ac90118b9e7a8 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -6083,6 +6083,7 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port) struct drm_dp_aux *immediate_upstream_aux; struct drm_dp_mst_port *fec_port; struct drm_dp_desc desc = {}; + u8 upstream_dsc; u8 endpoint_fec; u8 endpoint_dsc; @@ -6109,8 +6110,6 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port) /* DP-to-DP peer device */ if (drm_dp_mst_is_virtual_dpcd(immediate_upstream_port)) { - u8 upstream_dsc; - if (drm_dp_dpcd_read(&port->aux, DP_DSC_SUPPORT, &endpoint_dsc, 1) != 1) return NULL; @@ -6156,6 +6155,13 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port) if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD)) { u8 dpcd_ext[DP_RECEIVER_CAP_SIZE]; + if (drm_dp_dpcd_read(immediate_upstream_aux, + DP_DSC_SUPPORT, &upstream_dsc, 1) != 1) + return NULL; + + if (!(upstream_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED)) + return NULL; + if (drm_dp_read_dpcd_caps(immediate_upstream_aux, dpcd_ext) < 0) return NULL; -- 2.44.2
