On Mon, Oct 06, 2025 at 09:58:49AM +0530, Ankit Nautiyal wrote:
> As we move towards using a shorter, optimized guardband, we need to adjust
> how the delayed vblank start is computed.
>
> Introduce intel_crtc_compute_vrr_guardband() to handle guardband
> computation and apply vblank_start adjustment for platforms that always use
> the VRR timing generator.
>
> This function wraps the existing intel_vrr_compute_guardband() and adjusts
> crtc_vblank_start using (vblank_length - guardband) only when
> intel_vrr_always_use_vrr_tg() is true. Since the guardband is not yet
> optimized, the adjustment currently evaluates to zero, preserving existing
> behavior.
>
> This paves way for guardband optimization, by handling the movement of
> the crtc_vblank_start for platforms that have VRR TG always active.
>
> Also update allow_vblank_delay_fastset() to permit vblank delay adjustments
> during fastboot when VRR TG is always active, even without inherited state.
>
> Signed-off-by: Ankit Nautiyal <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 33 ++++++++++++++++++--
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index b2d4e24fd7c6..1964e41b5704 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2403,6 +2403,27 @@ static int
> intel_crtc_compute_set_context_latency(struct intel_atomic_state *sta
> return 0;
> }
>
> +static void intel_crtc_compute_vrr_guardband(struct intel_atomic_state
> *state,
> + struct intel_crtc *crtc)
Why this wrapper? You could just stick the adjustemnt into
intel_vrr_compute_guardband().
> +{
> + struct intel_display *display = to_intel_display(state);
> + struct intel_crtc_state *crtc_state =
> + intel_atomic_get_new_crtc_state(state, crtc);
> + struct drm_display_mode *adjusted_mode =
> + &crtc_state->hw.adjusted_mode;
> +
> + intel_vrr_compute_guardband(crtc_state);
> +
> + if (intel_vrr_always_use_vrr_tg(display)) {
> + int vblank_length = adjusted_mode->crtc_vtotal -
> + (crtc_state->set_context_latency +
> + adjusted_mode->crtc_vdisplay);
> +
> + adjusted_mode->crtc_vblank_start +=
> + vblank_length - crtc_state->vrr.guardband;
Why aren't you using the same 'vblank_start = vtotal-guardband' here as
during readout?
> + }
> +}
> +
> static int intel_crtc_compute_config(struct intel_atomic_state *state,
> struct intel_crtc *crtc)
> {
> @@ -2414,7 +2435,7 @@ static int intel_crtc_compute_config(struct
> intel_atomic_state *state,
> if (ret)
> return ret;
>
> - intel_vrr_compute_guardband(crtc_state);
> + intel_crtc_compute_vrr_guardband(state, crtc);
>
> ret = intel_dpll_crtc_compute_clock(state, crtc);
> if (ret)
> @@ -5105,9 +5126,15 @@ static bool allow_vblank_delay_fastset(const struct
> intel_crtc_state *old_crtc_s
> * Allow fastboot to fix up vblank delay (handled via LRR
> * codepaths), a bit dodgy as the registers aren't
> * double buffered but seems to be working more or less...
> + *
> + * Also allow this when the VRR timing generator is always on,
> + * which implies optimized guardband is used. In such cases,
> + * vblank delay may vary even without inherited state, but it's
> + * still safe as VRR guardband is still same.
> */
> - return HAS_LRR(display) && old_crtc_state->inherited &&
> - !intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DSI);
> + return HAS_LRR(display) &&
> + (old_crtc_state->inherited ||
> intel_vrr_always_use_vrr_tg(display)) &&
> + !intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DSI);
This part doesn't seem directly related to the making crtc_vblank_start
correct. We still use the non-optimzied guardband so crtc_vblank_start
should not be changing during normal runtime operation.
> }
>
> bool
> --
> 2.45.2
--
Ville Syrjälä
Intel
