On Mon, May 20, 2024 at 09:57:59PM +0300, Imre Deak wrote: > Symbols consisting of multiple (4) TU timeslots may get split across > MTPs when using 2 or 1 link lanes. Avoid this, as required by Bspec by > aligning the allocated TUs to 2 when using 2 lanes and 4 when using 1 > lane. > > Atm, we also have to align the PBNs used to allocate BW along the MST > path, since DRM core keeps track of its own TU value, derived from the > PBN and that TU value must match what the driver calculates. > > On some platforms the alignment is only required on 8b/10b links, a > follow-up patch will remove the limitation for those. > > Bspec: 49266, 68922 > > Signed-off-by: Imre Deak <imre.d...@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrj...@linux.intel.com> > --- > drivers/gpu/drm/i915/display/intel_dp_mst.c | 27 ++++++++++++++++++--- > 1 file changed, 23 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c > b/drivers/gpu/drm/i915/display/intel_dp_mst.c > index c772ba19c5477..c9c5d235744ab 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c > @@ -207,6 +207,7 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct > intel_encoder *encoder, > int remote_bw_overhead; > int link_bpp_x16; > int remote_tu; > + fixed20_12 pbn; > > drm_dbg_kms(&i915->drm, "Trying bpp %d\n", bpp); > > @@ -237,11 +238,29 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct > intel_encoder *encoder, > * crtc_state->dp_m_n.tu), provided that the driver doesn't > * enable SSC on the corresponding link. > */ > - crtc_state->pbn = > intel_dp_mst_calc_pbn(adjusted_mode->crtc_clock, > - link_bpp_x16, > - remote_bw_overhead); > + pbn.full = > dfixed_const(intel_dp_mst_calc_pbn(adjusted_mode->crtc_clock, > + link_bpp_x16, > + > remote_bw_overhead)); > + remote_tu = DIV_ROUND_UP(pbn.full, mst_state->pbn_div.full); > > - remote_tu = DIV_ROUND_UP(dfixed_const(crtc_state->pbn), > mst_state->pbn_div.full); > + /* > + * Aligning the TUs ensures that symbols consisting of multiple > + * (4) symbol cycles don't get split between two consecutive > + * MTPs, as required by Bspec. > + * TODO: remove the alignment restriction for 128b/132b links > + * on some platforms, where Bspec allows this. > + */ > + remote_tu = ALIGN(remote_tu, 4 / crtc_state->lane_count); > + > + /* > + * Also align PBNs accordingly, since MST core will derive its > + * own copy of TU from the PBN in > drm_dp_atomic_find_time_slots(). > + * The above comment about the difference between the PBN > + * allocated for the whole path and the TUs allocated for the > + * first branch device's link also applies here. > + */ > + pbn.full = remote_tu * mst_state->pbn_div.full; > + crtc_state->pbn = dfixed_trunc(pbn); > > drm_WARN_ON(&i915->drm, remote_tu < crtc_state->dp_m_n.tu); > crtc_state->dp_m_n.tu = remote_tu; > -- > 2.43.3 -- Ville Syrjälä Intel
