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, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index bf170bd83ef7..2a45a25e42fb 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -7532,6 +7532,7 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
 	intel_atomic_commit_fence_wait(state);
 
 	drm_atomic_helper_wait_for_dependencies(&state->base);
+	drm_dp_mst_atomic_wait_for_dependencies(&state->base);
 
 	if (state->modeset)
 		wakeref = intel_display_power_get(dev_priv, POWER_DOMAIN_MODESET);
@@ -8600,6 +8601,10 @@ out:
 	return ret;
 }
 
+static const struct drm_mode_config_helper_funcs intel_mode_config_funcs = {
+	.atomic_commit_setup = drm_dp_mst_atomic_setup_commit,
+};
+
 static void intel_mode_config_init(struct drm_i915_private *i915)
 {
 	struct drm_mode_config *mode_config = &i915->drm.mode_config;
@@ -8614,6 +8619,7 @@ static void intel_mode_config_init(struct drm_i915_private *i915)
 	mode_config->prefer_shadow = 1;
 
 	mode_config->funcs = &intel_mode_funcs;
+	mode_config->helper_private = &intel_mode_config_funcs;
 
 	mode_config->async_page_flip = HAS_ASYNC_FLIPS(i915);