On Wed, Sep 24, 2025 at 04:21:26PM +0530, Ankit Nautiyal wrote: > Until LNL, intel_dsb_wait_vblanks() used to wait for the undelayed vblank > start. However, from PTL onwards, it waits for the start of the > safe-window defined by the number of lines programmed in the register > TRANS_SET_CONTEXT_LATENCY. This change was introduced to move the SCL > window out of the vblank region, supporting modes with higher refresh > rates and smaller vblanks. This change introduces a "safe window" a > scanline range from (undelayed vblank - SCL) to (delayed vblank - SCL). > > As a result, on PTL+ platforms, the DSB wait for vblank completes exactly > SCL lines earlier than the undelayed vblank start (safe window start). > If the flip occurs in the active region and the push happens before the > vmin decision boundary, the DSB wait fires early, and the push is sent > inside this safe window. In such cases, the push bit is cleared at the > delayed vblank, but our wait logic does not account for the early trigger, > leading to DSB poll errors. > > To fix this, we add an explicit wait for the end of the safe window i.e., > the scanline range from (undelayed vblank - SCL) to (delayed vblank - SCL). > Once past this window, we are exactly SCL lines away from the delayed > vblank, and our existing wait logic works as intended. > > This additional wait is only effective if the push occurs before the vmin > decision boundary. If the push happens after the boundary, the hardware > already guarantees we're SCL lines away from the delayed vblank, and the > extra wait becomes a no-op. > > v2: > - Use helpers for safe window start/end. (Ville) > - Move the extra wait inside the helper to wait for delayed vblank. (Ville) > - Update the commit message. > > v3: > - Add more documentation for explanation for the wait. (Ville) > - Rename intel_vrr_vmin_safe_window_start/end as this is vmin safe > window. (Ville) > - Minor refactoring to align with the code. (Ville) > - Update the commit message for more clarity. > > Signed-off-by: Ankit Nautiyal <[email protected]> > --- > drivers/gpu/drm/i915/display/intel_dsb.c | 16 ++++++++++++++++ > drivers/gpu/drm/i915/display/intel_vrr.c | 17 +++++++++++++++++ > drivers/gpu/drm/i915/display/intel_vrr.h | 2 ++ > 3 files changed, 35 insertions(+) > > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c > b/drivers/gpu/drm/i915/display/intel_dsb.c > index 135d40852e4c..3cb4c9be146f 100644 > --- a/drivers/gpu/drm/i915/display/intel_dsb.c > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c > @@ -824,6 +824,22 @@ void intel_dsb_wait_for_delayed_vblank(struct > intel_atomic_state *state, > int usecs = intel_scanlines_to_usecs(&crtc_state->hw.adjusted_mode, > dsb_vblank_delay(state, crtc)); > > + /* > + * If the push happened before the vmin decision boundary > + * we don't know how far we are from the undelayed vblank. > + * Wait until we're past the vmin safe window, at which > + * point we're SCL lines away from the delayed vblank. > + * > + * If the push happened after the vmin decision boundary > + * the hardware itself guarantees that we're SCL lines > + * away from the delayed vblank, and we won't be inside > + * the vmin safe window so this extra wait does nothing. > + */ > + if (pre_commit_is_vrr_active(state, crtc)) > + intel_dsb_wait_scanline_out(state, dsb, > + > intel_vrr_vmin_safe_window_start(crtc_state), > + > intel_vrr_vmin_safe_window_end(crtc_state));
Hmm, I thought we already had a 'if (vrr)' check here. But I guess that was in dsb_vblank_delay(). Hmm, yeah I think what you did here is fine for the moment. I'm thinking we should follow up with inlining dsb_vblank_delay() directly into intel_dsb_wait_for_delayed_vblank(), just to keep all the VRR related wait magic in one place. I don't think there are any other users of dsb_vblank_delay(). > + > intel_dsb_wait_usec(dsb, usecs); > } > > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c > b/drivers/gpu/drm/i915/display/intel_vrr.c > index 1bb9db06f43d..26c5c32a9a58 100644 > --- a/drivers/gpu/drm/i915/display/intel_vrr.c > +++ b/drivers/gpu/drm/i915/display/intel_vrr.c > @@ -800,3 +800,20 @@ void intel_vrr_get_config(struct intel_crtc_state > *crtc_state) > if (crtc_state->vrr.enable) > crtc_state->mode_flags |= I915_MODE_FLAG_VRR; > } > + > +int intel_vrr_vmin_safe_window_start(const struct intel_crtc_state > *crtc_state) I only wanted you to rename the safe_window_end(). The safe window start doesn't change for vmin/vmax/etc. So should drop the "vmin" again from this one. With that Reviewed-by: Ville Syrjälä <[email protected]> > +{ > + struct intel_display *display = to_intel_display(crtc_state); > + > + if (DISPLAY_VER(display) >= 30) > + return crtc_state->hw.adjusted_mode.crtc_vdisplay - > + crtc_state->set_context_latency; > + else > + return crtc_state->hw.adjusted_mode.crtc_vdisplay; > +} > + > +int intel_vrr_vmin_safe_window_end(const struct intel_crtc_state *crtc_state) > +{ > + return intel_vrr_vmin_vblank_start(crtc_state) - > + crtc_state->set_context_latency; > +} > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.h > b/drivers/gpu/drm/i915/display/intel_vrr.h > index 38bf9996b883..239e4f94725c 100644 > --- a/drivers/gpu/drm/i915/display/intel_vrr.h > +++ b/drivers/gpu/drm/i915/display/intel_vrr.h > @@ -41,5 +41,7 @@ void intel_vrr_transcoder_enable(const struct > intel_crtc_state *crtc_state); > void intel_vrr_transcoder_disable(const struct intel_crtc_state *crtc_state); > void intel_vrr_set_fixed_rr_timings(const struct intel_crtc_state > *crtc_state); > bool intel_vrr_always_use_vrr_tg(struct intel_display *display); > +int intel_vrr_vmin_safe_window_start(const struct intel_crtc_state > *crtc_state); > +int intel_vrr_vmin_safe_window_end(const struct intel_crtc_state > *crtc_state); > > #endif /* __INTEL_VRR_H__ */ > -- > 2.45.2 -- Ville Syrjälä Intel
