On Mon, Jan 25, 2021 at 05:55:03PM -0500, Lyude Paul wrote: > On Mon, 2021-01-25 at 23:04 +0200, Imre Deak wrote: > > On Mon, Jan 25, 2021 at 02:24:58PM -0500, Lyude Paul wrote: > > > 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) > > > > I thought (as a follow-up work) that drm_dp_atomic_find_vcpi_slots() and > > drm_dp_mst_allocate_vcpi() could be made more generic, requiring the > > drivers to always pass in pbn_div. By that we could remove > > mst_mgr::pbn_div, keeping only one copy of this value (the one passed to > > the above functions). > > I'm fine with that! The only thing I ask is (even though it's taken forever) we > are eventually planning on making it so that we'll have MST helpers that can > suggest changing the PBN divisor in order to implement link fallback retraining. > As long as we're still able to make that work in the future, I'm totally fine > with this. I don't see a problem wrt. link retraining, pbn_div passed to the above functions should just reflect the actual rate and lane count the link was trained with. > > > 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! > > > > > > > -- > 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! >
