On Mon, 2021-01-25 at 19:36 +0200, Imre Deak wrote: > Atm the driver will calculate a wrong MST timeslots/MTP (aka time unit) > value for MST streams if the link parameters (link rate or lane count) > are limited in a way independent of the sink capabilities (reported by > DPCD). > > One example of such a limitation is when a MUX between the sink and > source connects only a limited number of lanes to the display and > connects the rest of the lanes to other peripherals (USB). > > Another issue is that atm MST core calculates the divider based on the > backwards compatible DPCD (at address 0x0000) vs. the extended > capability info (at address 0x2200). This can result in leaving some > part of the MST BW unused (For instance in case of the WD19TB dock). > > Fix the above two issues by calculating the PBN divider value based on > the rate and lane count link parameters that the driver uses for all > other computation. > > Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/2977 > Cc: Lyude Paul <lyude@xxxxxxxxxx> > Cc: Ville Syrjala <ville.syrjala@xxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > --- > drivers/gpu/drm/i915/display/intel_dp_mst.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c > b/drivers/gpu/drm/i915/display/intel_dp_mst.c > index d6a1b961a0e8..b4621ed0127e 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c > @@ -68,7 +68,9 @@ static int intel_dp_mst_compute_link_config(struct > intel_encoder *encoder, > > slots = drm_dp_atomic_find_vcpi_slots(state, &intel_dp- > >mst_mgr, > connector->port, > - crtc_state->pbn, 0); > + crtc_state->pbn, > + > drm_dp_get_vc_payload_bw(crtc_state->port_clock, > + This patch looks fine, however you should take care to also update the documentation for drm_dp_atomic_find_vcpi_slots() so that it mentiones that pbn_div should be DSC aware but also is not exclusive to systems supporting DSC over MST (see the docs for the @pbn_div parameter) Thank you for doing this! I've been meaning to fix the WD19 issues for a while now but have been too bogged down by other stuff to spend any time on MST recently. > crtc_state->lane_count)); > if (slots == -EDEADLK) > return slots; > if (slots >= 0) -- Sincerely, Lyude Paul (she/her) Software Engineer at Red Hat Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've asked me a question, are waiting for a review/merge on a patch, etc. and I haven't responded in a while, please feel free to send me another email to check on my status. I don't bite!
