> -----Original Message-----
> From: Ville Syrjälä <[email protected]>
> Sent: Friday, 28 August 2026 21.38
> To: Kahola, Mika <[email protected]>
> Cc: [email protected]; [email protected]
> Subject: Re: [PATCH 2/3] drm/i915/display: Restrict flipq to simple
> single-plane updates
>
> On Fri, Aug 07, 2026 at 12:15:39PM +0000, Mika Kahola wrote:
> > Our flipq eligibility check is too loose: it still lets through
> > commits that change the active/enabled plane mask, or need extra
> > pipe/M-N/LRR/watermark programming. Those aren't simple queued plane
> > updates and have no business going through flipq.
> >
> > Found this chasing a CRC mismatch in kms_cursor_crc's
> > cursor-alpha-opaque: a plane enable/disable commit slipped through
> > flipq ahead of the plane-content commit the CRC actually checks.
> >
> > Reject flipq for anything touching more than one plane, changing the
> > active/enabled plane masks, or needing async flip, VRR, PSR, color,
> > pipe, M/N, LRR or watermark updates. More conservative than strictly
> > necessary in some cases, but better safe than racy.
> >
> > Assisted-by: Copilot:claude-sonnet-5
> > Signed-off-by: Mika Kahola <[email protected]>
> > ---
> > drivers/gpu/drm/i915/display/intel_display.c | 53 +++++++++++++++++---
> > 1 file changed, 46 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> > b/drivers/gpu/drm/i915/display/intel_display.c
> > index 5cdaa59f005e..2483c031631c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -7323,6 +7323,51 @@ static void
> > intel_atomic_prepare_plane_clear_colors(struct intel_atomic_state *s
> > }
> > }
> >
> > +static bool intel_flipq_commit_is_eligible(struct intel_atomic_state
> > *state,
> > + struct intel_crtc *crtc)
> > +{
> > + struct intel_display *display = to_intel_display(state);
> > + const struct intel_crtc_state *old_crtc_state =
> > + intel_atomic_get_old_crtc_state(state, crtc);
> > + const struct intel_crtc_state *new_crtc_state =
> > + intel_atomic_get_new_crtc_state(state, crtc);
> > +
> > + if (!intel_flipq_supported(display))
> > + return false;
> > +
> > + if (intel_crtc_needs_modeset(new_crtc_state) ||
> > + intel_crtc_needs_fastset(new_crtc_state) ||
> > + intel_crtc_needs_color_update(new_crtc_state))
> > + return false;
> > +
> > + if (!new_crtc_state->update_planes ||
> > + !is_power_of_2(new_crtc_state->update_planes))
> > + return false;
>
> The number of planes being updated doesn't matter.
Right. Removing these.
>
> > +
> > + if (new_crtc_state->do_async_flip ||
> > + new_crtc_state->vrr.enable ||
> > + new_crtc_state->has_psr)
> > + return false;
> > +
> > + if (old_crtc_state->active_planes != new_crtc_state->active_planes ||
> > + old_crtc_state->enabled_planes != new_crtc_state->enabled_planes)
> > + return false;
>
> Enabling/disabling planes is perfectly fine.
Right, especially as the first patch of the series will be reworked , this is
not needed. Removing this as well.
>
> > +
> > + /*
> > + * Flipq is only suitable for simple queued single-plane updates
> > + * that do not change plane topology and do not require additional
> > + * pipe/timing/watermark programming.
> > + */
> > + if (new_crtc_state->update_pipe ||
> > + new_crtc_state->update_m_n ||
> > + new_crtc_state->update_lrr ||
> > + new_crtc_state->update_wm_pre ||
> > + new_crtc_state->update_wm_post)
>
> Those update_wm_* flags are just hacks for ancient platforms.
> Not relevant here.
Yes, these we don't need.
Thanks for the review!
-Mika-
>
> > + return false;
> > +
> > + return true;
> > +}
> > +
> > static void intel_atomic_dsb_prepare(struct intel_atomic_state *state,
> > struct intel_crtc *crtc)
> > {
> > @@ -7338,13 +7383,7 @@ static void intel_atomic_dsb_prepare(struct
> > intel_atomic_state *state,
> >
> > /* FIXME deal with everything */
> > new_crtc_state->use_flipq =
> > - intel_flipq_supported(display) &&
> > - !new_crtc_state->do_async_flip &&
> > - !new_crtc_state->vrr.enable &&
> > - !new_crtc_state->has_psr &&
> > - !intel_crtc_needs_modeset(new_crtc_state) &&
> > - !intel_crtc_needs_fastset(new_crtc_state) &&
> > - !intel_crtc_needs_color_update(new_crtc_state);
> > + intel_flipq_commit_is_eligible(state, crtc);
> >
> > new_crtc_state->use_dsb =
> > !new_crtc_state->use_flipq &&
> > --
> > 2.43.0
>
> --
> Ville Syrjälä
> Intel
