On Sun, Sep 28, 2025 at 12:35:40PM +0530, Ankit Nautiyal wrote:
> As we move towards using a shorter, optimized guardband, we need to adjust
> how the delayed vblank start is computed.
>
> Use the helper intel_vrr_compute_guardband() to calculate the optimized
> guardband. Since this is measured from the vblank end, we shift the
> vblank-start accordingly.
>
> Calculate the minimum delay required based on the guardband and apply it in
> intel_crtc_vblank_delay() to update crtc_vblank_start.
>
> Additionally, introduce a new allow_vblank_delay_fastset() helper that
> combines the existing LRR-based logic with an additional check for the
> optimized guardband usage.
>
> v2:
> - Check if optimized guardband is more than vblank length and add debug
> print.
> - Extend vblank delay fastset logic to cover optimized guardband.
>
> Signed-off-by: Ankit Nautiyal <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 79 +++++++++++++++++++-
> 1 file changed, 76 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index 4135f9be53fd..97a3121a204f 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2361,6 +2361,67 @@ static int intel_crtc_compute_pipe_mode(struct
> intel_crtc_state *crtc_state)
> return 0;
> }
>
> +static
> +int intel_crtc_min_guardband_delay(struct intel_atomic_state *state,
> + struct intel_crtc *crtc)
> +{
> + struct intel_display *display = to_intel_display(state);
> + struct intel_crtc_state *crtc_state =
> + intel_atomic_get_new_crtc_state(state, crtc);
> + const struct drm_display_mode *adjusted_mode =
> + &crtc_state->hw.adjusted_mode;
> + struct drm_connector_state *conn_state;
> + struct drm_connector *drm_connector;
> + int vblank_length;
> + int i;
> +
> + if (!intel_vrr_use_optimized_guardband(crtc_state))
> + return 0;
> +
> + vblank_length = crtc_state->vrr.vmin -
> + adjusted_mode->crtc_vdisplay;
> +
> + for_each_new_connector_in_state(&state->base,
> + drm_connector,
> + conn_state, i) {
> + int guardband;
> + struct intel_connector *connector;
> +
> + if (conn_state->crtc != &crtc->base)
> + continue;
> +
> + connector = to_intel_connector(drm_connector);
> + guardband = intel_vrr_compute_guardband(crtc_state,
> + connector);
> + if (guardband > vblank_length) {
> + drm_dbg_kms(display->drm,
> + "[CRTC:%d:%s] Cannot optimize guardband
> (%d) exceeds max (%d)\n",
> + crtc->base.base.id, crtc->base.name,
> + guardband,
> + vblank_length);
> + return 0;
> + }
> +
> + return vblank_length - guardband;
> + }
> +
> + return 0;
> +}
> +
> +static void intel_crtc_vblank_delay(struct intel_atomic_state *state,
> + struct intel_crtc *crtc)
> +{
> + 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;
> + int vblank_delay = 0;
> +
> + vblank_delay = intel_crtc_min_guardband_delay(state, crtc);
> +
> + adjusted_mode->crtc_vblank_start += vblank_delay;
> +}
> +
> static int intel_crtc_set_context_latency(struct intel_crtc_state
> *crtc_state)
> {
> struct intel_display *display = to_intel_display(crtc_state);
> @@ -2413,6 +2474,7 @@ static int intel_crtc_compute_config(struct
> intel_atomic_state *state,
> ret = intel_crtc_compute_set_context_latency(state, crtc);
> if (ret)
> return ret;
> + intel_crtc_vblank_delay(state, crtc);
IMO we should get rid of all this vblank_delay terminology here.
This one I think should just be our current
intel_vrr_compute_config_late() (renamed to eg.
intel_vrr_compute_guardband()).
After which we just have to solve all the chicken vs. egg problems
to really compute the approriate optimized guardband value.
> ret = intel_dpll_crtc_compute_clock(state, crtc);
> if (ret)
> @@ -5101,13 +5163,24 @@ static bool allow_vblank_delay_fastset_lrr(const
> struct intel_crtc_state *old_cr
> {
> struct intel_display *display = to_intel_display(old_crtc_state);
>
> + return HAS_LRR(display) && old_crtc_state->inherited &&
> + !intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DSI);
> +}
> +
> +static bool allow_vblank_delay_fastset(const struct intel_crtc_state
> *old_crtc_state,
> + const struct intel_crtc_state
> *new_crtc_state)
> +{
> /*
> * 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...
> + *
> + * Additionally, with the optimized guardband the vblank start
> + * is moved further away from the undelayed vblank. Allow this
> + * vblank delay when optimized guardband is used.
> */
> - return HAS_LRR(display) && old_crtc_state->inherited &&
> - !intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DSI);
> + return allow_vblank_delay_fastset_lrr(old_crtc_state) ||
> + intel_vrr_use_optimized_guardband(new_crtc_state);
> }
>
> bool
> @@ -5242,7 +5315,7 @@ intel_pipe_config_compare(const struct intel_crtc_state
> *current_config,
> PIPE_CONF_CHECK_I(name.crtc_hsync_start); \
> PIPE_CONF_CHECK_I(name.crtc_hsync_end); \
> PIPE_CONF_CHECK_I(name.crtc_vdisplay); \
> - if (!fastset || !allow_vblank_delay_fastset_lrr(current_config)) \
> + if (!fastset || !allow_vblank_delay_fastset(current_config,
> pipe_config)) \
> PIPE_CONF_CHECK_I(name.crtc_vblank_start); \
> PIPE_CONF_CHECK_I(name.crtc_vsync_start); \
> PIPE_CONF_CHECK_I(name.crtc_vsync_end); \
> --
> 2.45.2
--
Ville Syrjälä
Intel
