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, 7 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 1d54f2cd38b2..c55af5d78ea2 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -2136,6 +2136,7 @@ nv50_disp_atomic_commit_tail(struct drm_atomic_state *state)
 	nv50_crc_atomic_stop_reporting(state);
 	drm_atomic_helper_wait_for_fences(dev, state, false);
 	drm_atomic_helper_wait_for_dependencies(state);
+	drm_dp_mst_atomic_wait_for_dependencies(state);
 	drm_atomic_helper_update_legacy_modeset_state(dev, state);
 	drm_atomic_helper_calc_timestamping_constants(state);
 
@@ -2616,6 +2617,11 @@ nv50_disp_func = {
 	.atomic_state_free = nv50_disp_atomic_state_free,
 };
 
+static const struct drm_mode_config_helper_funcs
+nv50_disp_helper_func = {
+	.atomic_commit_setup = drm_dp_mst_atomic_setup_commit,
+};
+
 /******************************************************************************
  * Init
  *****************************************************************************/
@@ -2699,6 +2705,7 @@ nv50_display_create(struct drm_device *dev)
 	nouveau_display(dev)->fini = nv50_display_fini;
 	disp->disp = &nouveau_display(dev)->disp;
 	dev->mode_config.funcs = &nv50_disp_func;
+	dev->mode_config.helper_private = &nv50_disp_helper_func;
 	dev->mode_config.quirk_addfb_prefer_xbgr_30bpp = true;
 	dev->mode_config.normalize_zpos = true;