[PATCH 2/2] drm/i915/dp_mst: Fix configuring TUs for a disconnected stream

[Imre Deak <imre.deak@intel.com>]

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
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 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);
-- 
2.49.1