Re: [PATCH 13/14] drm/i915/dp_mst: Ensure link parameters are up-to-date for a disabled link

[Imre Deak <imre.deak@intel.com>]

On Thu, Jul 25, 2024 at 08:26:38AM +0300, Kandpal, Suraj wrote:
> 
> 
> > -----Original Message-----
> > From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Imre
> > Deak
> > Sent: Monday, July 22, 2024 10:25 PM
> > To: intel-gfx@lists.freedesktop.org
> > Subject: [PATCH 13/14] drm/i915/dp_mst: Ensure link parameters are up-to-
> > date for a disabled link
> >
> > As explained in the previous patch, the MST link BW reported by branch
> > devices during topology probing/path resources enumeration depends on
> > the link parameters programmed to DPCD to be up-to-date. After a sink is
> 
> I think you maybe missed a couple of words here maybe fix that

Not sure, it looks ok to me.

> Rest LGTM
> Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
> 
> > plugged this is not ensured, as those DPCD values start out zeroed. The
> > target link parameters (for a subsequent modeset) are the maximum that is
> > supported, so make sure these maximum values are programmed before
> > the topology probing.
> >
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c     |  3 ++
> >  drivers/gpu/drm/i915/display/intel_dp_mst.c | 31 +++++++++++++++++++++
> > drivers/gpu/drm/i915/display/intel_dp_mst.h |  1 +
> >  3 files changed, 35 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 0771e4c6357ba..41f5d82ca75d8 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4262,6 +4262,9 @@ intel_dp_mst_configure(struct intel_dp *intel_dp)
> >
> >       intel_dp->is_mst = intel_dp->mst_detect != DRM_DP_SST;
> >
> > +     if (intel_dp->is_mst)
> > +             intel_dp_mst_prepare_probe(intel_dp);
> > +
> >       drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp-
> > >is_mst);
> >
> >       /* Avoid stale info on the next detect cycle. */ diff --git
> > a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > index 19c8b6878b030..faee7af0a8a48 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > @@ -43,6 +43,7 @@
> >  #include "intel_dp_hdcp.h"
> >  #include "intel_dp_mst.h"
> >  #include "intel_dp_tunnel.h"
> > +#include "intel_dp_link_training.h"
> >  #include "intel_dpio_phy.h"
> >  #include "intel_hdcp.h"
> >  #include "intel_hotplug.h"
> > @@ -2031,3 +2032,33 @@ bool intel_dp_mst_crtc_needs_modeset(struct
> > intel_atomic_state *state,
> >
> >       return false;
> >  }
> > +
> > +/**
> > + * intel_dp_mst_prepare_probe - Prepare an MST link for topology
> > +probing
> > + * @intel_dp: DP port object
> > + *
> > + * Prepare an MST link for topology probing, programming the target
> > + * link parameters to DPCD. This step is a requirement of the
> > +enumaration
> > + * of path resources during probing.
> > + */
> > +void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp) {
> > +     int link_rate = intel_dp_max_link_rate(intel_dp);
> > +     int lane_count = intel_dp_max_lane_count(intel_dp);
> > +     u8 rate_select;
> > +     u8 link_bw;
> > +
> > +     if (intel_dp->link_trained)
> > +             return;
> > +
> > +     if (intel_mst_probed_link_params_valid(intel_dp, link_rate,
> > lane_count))
> > +             return;
> > +
> > +     intel_dp_compute_rate(intel_dp, link_rate, &link_bw, &rate_select);
> > +
> > +     intel_dp_link_training_set_mode(intel_dp, link_rate, false);
> > +     intel_dp_link_training_set_bw(intel_dp, link_bw, rate_select,
> > lane_count,
> > +                                   drm_dp_enhanced_frame_cap(intel_dp-
> > >dpcd));
> > +
> > +     intel_mst_set_probed_link_params(intel_dp, link_rate, lane_count);
> > }
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.h
> > b/drivers/gpu/drm/i915/display/intel_dp_mst.h
> > index 8ca1d599091c6..fba76454fa67f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.h
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.h
> > @@ -27,5 +27,6 @@ int intel_dp_mst_atomic_check_link(struct
> > intel_atomic_state *state,
> >                                  struct intel_link_bw_limits *limits);  bool
> > intel_dp_mst_crtc_needs_modeset(struct intel_atomic_state *state,
> >                                    struct intel_crtc *crtc);
> > +void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp);
> >
> >  #endif /* __INTEL_DP_MST_H__ */
> > --
> > 2.44.2
>