On Mon, Feb 12, 2024 at 05:30:40PM +0200, Jani Nikula wrote: > On Fri, 02 Feb 2024, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > On Fri, Feb 02, 2024 at 04:05:34PM +0200, Jani Nikula wrote: > >> If the sink supports 128b/132b and single-stream sideband messaging, > >> enable MST mode. > >> > >> With this, the topology manager will still write DP_MSTM_CTRL, which > >> should be ignored by the sink. In the future, > >> drm_dp_mst_topology_mgr_set_mst() bool mst_state parameter should > >> probably be turned into an enum drm_dp_mst_mode mst_mode parameter. > > > > Rather I'd say the topology manager should stop concerning itself > > with the MST enable bit and just frob the sideband enable bit. > > The MST enable bit should be configured at modeset time to > > reflect whether we're about to transmit in MST or SST mode. > > Are you suggesting the driver should write the MST vs. SST mode in > DP_MSTM_CTRL? Either that or there needs to be a function provided by the topology manager that gets called at modeset time to configure it. I don't recall when exactly it should be configured according the DP spec. > > I worry a bit about the rmw on DPCD regs. The topology manager only does > writes. > > BR, > Jani. > > > > > > > > >> > >> Cc: Arun R Murthy <arun.r.murthy@xxxxxxxxx> > >> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > >> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> > >> --- > >> drivers/gpu/drm/i915/display/intel_dp.c | 4 +++- > >> 1 file changed, 3 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c > >> index 4dd9c50226d1..16130e87dc23 100644 > >> --- a/drivers/gpu/drm/i915/display/intel_dp.c > >> +++ b/drivers/gpu/drm/i915/display/intel_dp.c > >> @@ -4020,7 +4020,9 @@ static bool intel_dp_mst_detect(struct intel_dp *intel_dp) > >> > >> intel_dp->is_mst = i915->display.params.enable_dp_mst && > >> intel_dp_mst_source_support(intel_dp) && > >> - sink_mst_mode == DP_MST_CAPABLE; > >> + (sink_mst_mode == DP_MST_CAPABLE || > >> + (sink_mst_mode == DP_MST_SIDEBAND_MSG && > >> + intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B)); > >> > >> drm_dbg_kms(&i915->drm, > >> "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s -> enable: %s\n", > >> -- > >> 2.39.2 > > -- > Jani Nikula, Intel -- Ville Syrjälä Intel
