On Thu, 2026-09-10 at 14:11 +0300, Imre Deak wrote: > On Thu, Sep 10, 2026 at 12:50:16PM +0300, Luca Coelho wrote: > > On Mon, 2026-09-07 at 20:44 +0300, Imre Deak wrote: > > > During an atomic commit after all the MST stream CRTC state is computed > > > the driver ensures that the sum of TUs of all the streams on a given MST > > > topology link is within limits (63 for 8b10 and 64 for 128b132b). For a > > > disconnected stream the DRM MST core's BW verification doesn't ensure > > > this, because the topology state it uses for this is destroyed as soon > > > as the stream (i.e. MST connector/port) is disconnected. The driver > > > should keep the link state valid even for such disconnected streams, as > > > userspace may disable them one-by-one only in a deferred way. Ensure the > > > link's sum of TUs stays within limits in this case by simply reusing the > > > maximum link BPP limit from the stream's (i.e. CRTC's) old state. > > > > > > The disconnection can happen either via the whole topology getting > > > disconnected or via only the given stream's port getting disconnected. > > > Check for both of these conditions separately, as a connector gets > > > unregistered after a link disconnect event only in a deferred way. > > > > > > Cc: [email protected] # v6.10+ > > > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16073 > > > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16384 > > > Signed-off-by: Imre Deak <[email protected]> > > > --- > > > drivers/gpu/drm/i915/display/intel_dp_mst.c | 21 ++++++++++++++++++++ > > > drivers/gpu/drm/i915/display/intel_dp_mst.h | 2 ++ > > > drivers/gpu/drm/i915/display/intel_link_bw.c | 3 ++- > > > 3 files changed, 25 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 20766b6c0bcfa..0c362784afe4a 100644 > > > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c > > > @@ -2172,6 +2172,27 @@ bool intel_dp_mst_crtc_needs_modeset(struct > > > intel_atomic_state *state, > > > return false; > > > } > > > > > > +bool intel_dp_mst_stream_disconnected(struct intel_atomic_state *state, > > > + const struct intel_crtc *crtc) > > > +{ > > > + struct intel_connector *connector; > > > + > > > + connector = get_connector_in_state_for_crtc(state, crtc); > > > + if (!connector) > > > + return false; > > > + > > > + if (!connector->mst.dp) > > > + return false; > > > + > > > + if (!connector->mst.dp->mst.mgr.mst_state) > > > + return true; > > > + > > > + if (drm_connector_is_unregistered(&connector->base)) > > > + return true; > > > + > > > + return false; > > > +} > > > + > > > /** > > > * intel_dp_mst_prepare_probe - Prepare an MST link for topology probing > > > * @intel_dp: DP port object > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.h > > > b/drivers/gpu/drm/i915/display/intel_dp_mst.h > > > index ab09b487c6bb5..8ce89242c05c9 100644 > > > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.h > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.h > > > @@ -28,6 +28,8 @@ 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); > > > +bool intel_dp_mst_stream_disconnected(struct intel_atomic_state *state, > > > + const struct intel_crtc *crtc); > > > void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp); > > > bool intel_dp_mst_verify_dpcd_state(struct intel_dp *intel_dp); > > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_link_bw.c > > > b/drivers/gpu/drm/i915/display/intel_link_bw.c > > > index b47474a3e9fec..e71e76d6fd3e0 100644 > > > --- a/drivers/gpu/drm/i915/display/intel_link_bw.c > > > +++ b/drivers/gpu/drm/i915/display/intel_link_bw.c > > > @@ -64,7 +64,8 @@ void intel_link_bw_init_limits(struct > > > intel_atomic_state *state, > > > intel_atomic_get_new_crtc_state(state, crtc); > > > int forced_bpp_x16 = get_forced_link_bpp_x16(state, crtc); > > > > > > - if (state->base.duplicated && crtc_state) { > > > + if ((state->base.duplicated && crtc_state) || > > > + intel_dp_mst_stream_disconnected(state, crtc)) { > > > limits->max_bpp_x16[pipe] = > > > crtc_state->max_link_bpp_x16; > > > if (intel_dsc_enabled_on_link(crtc_state)) > > > limits->link_dsc_pipes |= BIT(pipe); > > > > I think Sashiko's NULL-dereference commment is valid. Can you check > > it? > > At least I can't see how a connector can get into the atomic state > without the crtc state for the CRTC associated with the connector. > Sashiko didn't provide the exact scenario it had in mind.
As discussed offline, this is not really a problem, and it's a safe bypass the NULL pointer check here. Reviewed-by: Luca Coelho <[email protected]> -- Cheers, Luca.
