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Wed, 30 Sep 2026 09:54:42 -0400 (EDT) Date: Wed, 30 Sep 2026 15:54:37 +0200 From: Greg KH To: Sasha Levin Cc: stable@vger.kernel.org, Imre Deak , Luca Coelho , Jani Nikula Subject: Re: [PATCH 6.12.y] drm/i915/dp_mst: Fix configuring TUs for a disconnected stream Message-ID: <2026093033-ravioli-rectify-dc1e@gregkh> References: <2026092957-hardening-slingshot-e073@gregkh> <20260929193021.823447-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260929193021.823447-1-sashal@kernel.org> On Tue, Sep 29, 2026 at 03:30:21PM -0400, Sasha Levin wrote: > From: Imre Deak > > [ Upstream commit a443e0b8d647c1401b110d9f919d8c6cb8607260 ] > > 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: stable@vger.kernel.org # v6.10+ > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16073 > Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16384 > Reviewed-by: Luca Coelho > Signed-off-by: Imre Deak > Link: https://patch.msgid.link/20260907174413.741851-2-imre.deak@intel.com > (cherry picked from commit ee00f8fbb2b202002ab90834e02e9ba372773a36) > Signed-off-by: Jani Nikula > [ adapted MST field accesses to `mst_port` and `mst_mgr`, reusing a local `crtc` lookup. ] > Signed-off-by: Sasha Levin > --- > 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 | 7 ++++--- > 3 files changed, 27 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c > index eeaedd979354b..eb0ee759569c3 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c > @@ -2053,6 +2053,27 @@ 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_port) > + return false; > + > + if (!connector->mst_port->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 8343804ce3f8d..261a97e24d91e 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.h > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.h > @@ -27,6 +27,8 @@ 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 e7a9b860fac6e..da4f0186311ba 100644 > --- a/drivers/gpu/drm/i915/display/intel_link_bw.c > +++ b/drivers/gpu/drm/i915/display/intel_link_bw.c > @@ -32,11 +32,12 @@ void intel_link_bw_init_limits(struct intel_atomic_state *state, > limits->force_fec_pipes = 0; > limits->bpp_limit_reached_pipes = 0; > for_each_pipe(display, pipe) { > + struct intel_crtc *crtc = intel_crtc_for_pipe(i915, pipe); > const struct intel_crtc_state *crtc_state = > - intel_atomic_get_new_crtc_state(state, > - intel_crtc_for_pipe(i915, pipe)); > + intel_atomic_get_new_crtc_state(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 (crtc_state->fec_enable) > limits->force_fec_pipes |= BIT(pipe); > -- > 2.53.0 > > Breaks the build :(