> -----Original Message----- > From: Nikula, Jani <jani.nikula@xxxxxxxxx> > Sent: Tuesday, January 9, 2024 2:59 PM > To: Murthy, Arun R <arun.r.murthy@xxxxxxxxx>; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; > Deak, Imre <imre.deak@xxxxxxxxx> > Subject: RE: [PATCH] drm/i915/display/dp: 128/132b DP-capable with SST > > On Tue, 09 Jan 2024, Jani Nikula <jani.nikula@xxxxxxxxx> wrote: > > On Tue, 09 Jan 2024, "Murthy, Arun R" <arun.r.murthy@xxxxxxxxx> wrote: > >>> -----Original Message----- > >>> From: Nikula, Jani <jani.nikula@xxxxxxxxx> > >>> Sent: Monday, January 8, 2024 7:01 PM > >>> To: Murthy, Arun R <arun.r.murthy@xxxxxxxxx>; > >>> intel-gfx@xxxxxxxxxxxxxxxxxxxxx; Deak, Imre <imre.deak@xxxxxxxxx> > >>> Cc: Murthy, Arun R <arun.r.murthy@xxxxxxxxx> > >>> Subject: Re: [PATCH] drm/i915/display/dp: 128/132b DP-capable with > >>> SST > >>> > >>> On Wed, 03 Jan 2024, Arun R Murthy <arun.r.murthy@xxxxxxxxx> wrote: > >>> > With a value of '0' read from MSTM_CAP register MST to be enabled. > >>> > DP2.1 SCR updates the spec for 128/132b DP capable supporting only > >>> > one stream and not supporting single stream sideband MSG. > >>> > The underlying protocol will be MST to enable use of MTP. > >>> > > >>> > Signed-off-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx> > >>> > --- > >>> > drivers/gpu/drm/i915/display/intel_dp.c | 9 +++++++-- > >>> > 1 file changed, 7 insertions(+), 2 deletions(-) > >>> > > >>> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c > >>> > b/drivers/gpu/drm/i915/display/intel_dp.c > >>> > index 9ff0cbd9c0df..40d3280f8d98 100644 > >>> > --- a/drivers/gpu/drm/i915/display/intel_dp.c > >>> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c > >>> > @@ -4038,8 +4038,13 @@ intel_dp_configure_mst(struct intel_dp > *intel_dp) > >>> > if (!intel_dp_mst_source_support(intel_dp)) > >>> > return; > >>> > > >>> > - intel_dp->is_mst = sink_can_mst && > >>> > - i915->display.params.enable_dp_mst; > >>> > + /* > >>> > + * Even if dpcd reg MSTM_CAP is 0, if the sink supports UHBR > >>> > + rates > >>> then > >>> > + * DP2.1 can be enabled with underlying protocol using MST for MTP > >>> > + */ > >>> > + intel_dp->is_mst = (sink_can_mst || > >>> > + > >>> drm_dp_is_uhbr_rate(intel_dp_max_common_rate(intel_dp))) > >>> > + && i915->display.params.enable_dp_mst; > >>> > >>> We use drm_dp_is_uhbr_rate() in intel_dp_is_uhbr() to determine > >>> whether the link rate in the *crtc state* is uhbr, and by proxy > >>> whether the link in the *crtc > >>> state* is 128b/132b. > >>> > >> Yes! If the link rate in crtc_state is not uhbr then we dont enable 128/132b. > Also the return from drm_dp_read_mst_cap() return 0 or 1 and if not mst then > 128/132b is not enabled. We need to deviate here and a value of bit[0]=0, > bit[1]=0 in MSTM_CAP register is 128/132b with SST. Hence this hack is added > to see if the return from MSTM_CAP is 0x00 and if uhbr rates are supported > then enable 128/132b. > > > > Per spec it depends on intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & > > DP_CAP_ANSI_128B132B, why not use that here too? > > Also, shouldn't we ensure we don't try to do more than one stream? > Yes, this will be taken care of in a separate patch, tracked as part of separate JIRA. VLK-55112. Thanks and Regards, Arun R Murthy -------------------- > > > >> > >>> There, we've already decided to use uhbr and 128b/132b. > >>> > >>> This one here is different, and I think it's taking us to the wrong > >>> direction. For example, it should be possible to downgrade the link > >>> from uhbr to non-uhbr on link failures. We don't have that yet. But > >>> this makes untangling that even harder. > >> > >> Yes upon having the fallback, I think we will have to handle fallback in this > case separately. Change might be required in drm core, > drm_dp_read_mst_cap() should consider the DP2.1 changes to accommodate > this 0x00 value. > >> > >> Will be floating the fallback patches very soon. > >> > >> Thanks and Regards, > >> Arun R Murthy > >> -------------------- > >>> > >>> > >>> BR, > >>> Jani. > >>> > >>> > >>> > > >>> > drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, > >>> > intel_dp->is_mst); > >>> > >>> -- > >>> Jani Nikula, Intel > > -- > Jani Nikula, Intel
