drm/display/dp_mst: Add nonblocking helpers for DP MST

As Daniel Vetter pointed out, if we only use the atomic modesetting locks
with MST it's technically possible for a driver with non-blocking modesets
to race when it comes to MST displays - as we make the mistake of not doing
our own CRTC commit tracking in the topology_state object.

This could potentially cause problems if something like this happens:

* User starts non-blocking commit to disable CRTC-1 on MST topology 1
* User starts non-blocking commit to enable CRTC-2 on MST topology 1

There's no guarantee here that the commit for disabling CRTC-2 will only
occur after CRTC-1 has finished, since neither commit shares a CRTC - only
the private modesetting object for MST. Keep in mind this likely isn't a
problem for blocking modesets, only non-blocking.

So, begin fixing this by keeping track of which CRTCs on a topology have
changed by keeping track of which CRTCs we release or allocate timeslots
on. As well, add some helpers for:

* Setting up the drm_crtc_commit structs in the ->commit_setup hook
* Waiting for any CRTC dependencies from the previous topology state

v2:
* Use drm_dp_mst_atomic_setup_commit() directly - Jani

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/20220817193847.557945-9-lyude@redhat.com

1 files changed, 15 insertions, 0 deletions

diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
index 3b155ad3eee4..0ef7d0e6cf0c 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -581,6 +581,19 @@ struct drm_dp_mst_topology_state {
 	/** @mgr: The topology manager */
 	struct drm_dp_mst_topology_mgr *mgr;
 
+	/**
+	 * @pending_crtc_mask: A bitmask of all CRTCs this topology state touches, drivers may
+	 * modify this to add additional dependencies if needed.
+	 */
+	u32 pending_crtc_mask;
+	/**
+	 * @commit_deps: A list of all CRTC commits affecting this topology, this field isn't
+	 * populated until drm_dp_mst_atomic_wait_for_dependencies() is called.
+	 */
+	struct drm_crtc_commit **commit_deps;
+	/** @num_commit_deps: The number of CRTC commits in @commit_deps */
+	size_t num_commit_deps;
+
 	/** @total_avail_slots: The total number of slots this topology can handle (63 or 64) */
 	u8 total_avail_slots;
 	/** @start_slot: The first usable time slot in this topology (1 or 0) */
@@ -890,6 +903,8 @@ int __must_check
 drm_dp_atomic_release_time_slots(struct drm_atomic_state *state,
 				 struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port);
+void drm_dp_mst_atomic_wait_for_dependencies(struct drm_atomic_state *state);
+int __must_check drm_dp_mst_atomic_setup_commit(struct drm_atomic_state *state);
 int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port, bool power_up);
 int drm_dp_send_query_stream_enc_status(struct drm_dp_mst_topology_mgr *mgr,