drm/display/dp_mst: Add helpers for serializing SST <-> MST transitions

There's another kind of situation where we could potentially race with
nonblocking modesets and MST, especially if we were to only use the locking
provided by atomic modesetting:

* Display 1 begins as enabled on DP-1 in SST mode
* Display 1 switches to MST mode, exposes one sink in MST mode
* Userspace does non-blocking modeset to disable the SST display
* Userspace does non-blocking modeset to enable the MST display with a
  different CRTC, but the SST display hasn't been fully taken down yet
* Execution order between the last two commits isn't guaranteed since they
  share no drm resources

We can fix this however, by ensuring that we always pull in the atomic
topology state whenever a connector capable of driving an MST display
performs its atomic check - and then tracking CRTC commits happening on the
SST connector in the MST topology state. So, let's add some simple helpers
for doing that and hook them up in various drivers.

v2:
* Use intel_dp_mst_source_support() to check for MST support in i915, fixes
  CI failures

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220817193847.557945-14-lyude@redhat.com

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 32292c0be2bd..a4e113253df3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4992,12 +4992,21 @@ static int intel_dp_connector_atomic_check(struct drm_connector *conn,
 {
 	struct drm_i915_private *dev_priv = to_i915(conn->dev);
 	struct intel_atomic_state *state = to_intel_atomic_state(_state);
+	struct drm_connector_state *conn_state = drm_atomic_get_new_connector_state(_state, conn);
+	struct intel_connector *intel_conn = to_intel_connector(conn);
+	struct intel_dp *intel_dp = enc_to_intel_dp(intel_conn->encoder);
 	int ret;
 
 	ret = intel_digital_connector_atomic_check(conn, &state->base);
 	if (ret)
 		return ret;
 
+	if (intel_dp_mst_source_support(intel_dp)) {
+		ret = drm_dp_mst_root_conn_atomic_check(conn_state, &intel_dp->mst_mgr);
+		if (ret)
+			return ret;
+	}
+
 	/*
 	 * We don't enable port sync on BDW due to missing w/as and
 	 * due to not having adjusted the modeset sequence appropriately.