I -thought- I had fixed this entirely, but it looks like that I didn't test this thoroughly enough as we apparently still make one big mistake with nv50_msto_atomic_check() - we don't handle the following scenario:

* CRTC #1 has n VCPI allocated to it, is attached to connector DP-4 which is attached to encoder #1. enabled=y active=n * CRTC #1 is changed from DP-4 to DP-5, causing: * DP-4 crtc=#1→NULL (VCPI n→0) * DP-5 crtc=NULL→#1 * CRTC #1 steals encoder #1 back from DP-4 and gives it to DP-5 * CRTC #1 maintains the same mode as before, just with a different connector * mode_changed=n connectors_changed=y (we _SHOULD_ do VCPI 0→n here, but don't)

Once the above scenario is repeated once, we'll attempt freeing VCPI from the connector that we didn't allocate due to the connectors changing, but the mode staying the same. Sigh.

Since nv50_msto_atomic_check() has broken a few times now, let's rethink things a bit to be more careful: limit both VCPI/PBN allocations to mode_changed || connectors_changed, since neither VCPI or PBN should ever need to change outside of routing and mode changes.

Signed-off-by: Lyude Paul lyude@redhat.com Reported-by: Bohdan Milar bmilar@redhat.com Tested-by: Bohdan Milar bmilar@redhat.com Fixes: 232c9eec417a ("drm/nouveau: Use atomic VCPI helpers for MST") References: 412e85b60531 ("drm/nouveau: Only release VCPI slots on mode changes") Cc: Lyude Paul lyude@redhat.com Cc: Ben Skeggs bskeggs@redhat.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: David Airlie airlied@redhat.com Cc: Jerry Zuo Jerry.Zuo@amd.com Cc: Harry Wentland harry.wentland@amd.com Cc: Juston Li juston.li@intel.com Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Cc: Karol Herbst karolherbst@gmail.com Cc: Ilia Mirkin imirkin@alum.mit.edu Cc: stable@vger.kernel.org # v5.1+ --- drivers/gpu/drm/nouveau/dispnv50/disp.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c index 126703816794..5d23ab8e4917 100644 --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c @@ -771,16 +771,20 @@ nv50_msto_atomic_check(struct drm_encoder *encoder, struct nv50_head_atom *asyh = nv50_head_atom(crtc_state); int slots;

- /* When restoring duplicated states, we need to make sure that the - * bw remains the same and avoid recalculating it, as the connector's - * bpc may have changed after the state was duplicated - */ - if (!state->duplicated) - asyh->dp.pbn = - drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock, - connector->display_info.bpc * 3); + if (crtc_state->mode_changed || crtc_state->connectors_changed) { + /* + * When restoring duplicated states, we need to make sure that + * the bw remains the same and avoid recalculating it, as the + * connector's bpc may have changed after the state was + * duplicated + */ + if (!state->duplicated) { + const int bpp = connector->display_info.bpc * 3; + const int clock = crtc_state->adjusted_mode.clock; + + asyh->dp.pbn = drm_dp_calc_pbn_mode(bpp, clock); + }

- if (crtc_state->mode_changed) { slots = drm_dp_atomic_find_vcpi_slots(state, &mstm->mgr, mstc->port, asyh->dp.pbn);