Re: [PATCH 6.12.y] drm/i915/dp_mst: Fix configuring TUs for a disconnected stream

[Greg KH <greg@kroah.com>]

On Tue, Sep 29, 2026 at 03:30:21PM -0400, Sasha Levin wrote:
> From: Imre Deak <imre.deak@intel.com>
> 
> [ 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 <luciano.coelho@intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> Link: https://patch.msgid.link/20260907174413.741851-2-imre.deak@intel.com
> (cherry picked from commit ee00f8fbb2b202002ab90834e02e9ba372773a36)
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> [ adapted MST field accesses to `mst_port` and `mst_mgr`, reusing a local `crtc` lookup. ]
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  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 :(