On Wed, Sep 24, 2025 at 04:21:28PM +0530, Ankit Nautiyal wrote:
> The maximum guardband value is constrained by two factors:
> - The actual vblank length minus set context latency (SCL)
> - The hardware register field width:
> - 8 bits for ICL/TGL (VRR_CTL_PIPELINE_FULL_MASK -> max 255)
> - 16 bits for ADL+ (XELPD_VRR_CTL_VRR_GUARDBAND_MASK -> max 65535)
>
> Remove the #FIXME and clamp the guardband to the maximum allowed value.
>
> v2:
> - Use REG_FIELD_MAX(). (Ville)
> - Separate out functions for intel_vrr_max_guardband(),
> intel_vrr_max_vblank_guardband(). (Ville)
>
> v3:
> - Fix Typo: Add the missing adjusted_mode->crtc_vdisplay in guardband
> computation. (Ville)
> - Refactor intel_vrr_max_hw_guardband() and use else for consistency.
> (Ville)
>
> Signed-off-by: Ankit Nautiyal <[email protected]>
> Reviewed-by: Ville Syrjälä <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_vrr.c | 49 ++++++++++++++++++------
> 1 file changed, 37 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c
> b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 26c5c32a9a58..e29b4050a9df 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -409,6 +409,40 @@ intel_vrr_compute_config(struct intel_crtc_state
> *crtc_state,
> }
> }
>
> +static int
> +intel_vrr_max_hw_guardband(const struct intel_crtc_state *crtc_state)
> +{
> + struct intel_display *display = to_intel_display(crtc_state);
> + int max_pipeline_full = REG_FIELD_MAX(VRR_CTL_PIPELINE_FULL_MASK);
> + int max_guardband;
> +
> + if (DISPLAY_VER(display) >= 13)
> + max_guardband = REG_FIELD_MAX(XELPD_VRR_CTL_VRR_GUARDBAND_MASK);
> + else
> + max_guardband = intel_vrr_pipeline_full_to_guardband(crtc_state,
> +
> max_pipeline_full);
> + return max_guardband;
The 'max_guardband' variable looks useless here, could just return
directly from both sides of the if-else.
'max_pipeline_full' is perhaps redundant too, but I suppose the
line would get pretty long without it. So maybe it makes sense to keep
it.
> +}
> +
> +static int
> +intel_vrr_max_vblank_guardband(const struct intel_crtc_state *crtc_state)
> +{
> + struct intel_display *display = to_intel_display(crtc_state);
> + const struct drm_display_mode *adjusted_mode =
> &crtc_state->hw.adjusted_mode;
> +
> + return crtc_state->vrr.vmin -
> + adjusted_mode->crtc_vdisplay -
> + crtc_state->set_context_latency -
> + intel_vrr_extra_vblank_delay(display);
> +}
> +
> +static int
> +intel_vrr_max_guardband(struct intel_crtc_state *crtc_state)
> +{
> + return min(intel_vrr_max_hw_guardband(crtc_state),
> + intel_vrr_max_vblank_guardband(crtc_state));
> +}
> +
> void intel_vrr_compute_config_late(struct intel_crtc_state *crtc_state)
> {
> struct intel_display *display = to_intel_display(crtc_state);
> @@ -417,22 +451,13 @@ void intel_vrr_compute_config_late(struct
> intel_crtc_state *crtc_state)
> if (!intel_vrr_possible(crtc_state))
> return;
>
> - crtc_state->vrr.guardband =
> - crtc_state->vrr.vmin -
> - adjusted_mode->crtc_vdisplay -
> - crtc_state->set_context_latency -
> - intel_vrr_extra_vblank_delay(display);
> -
> - if (DISPLAY_VER(display) < 13) {
> - /* FIXME handle the limit in a proper way */
> - crtc_state->vrr.guardband =
> - min(crtc_state->vrr.guardband,
> - intel_vrr_pipeline_full_to_guardband(crtc_state,
> 255));
> + crtc_state->vrr.guardband = min(crtc_state->vrr.vmin -
> adjusted_mode->crtc_vdisplay,
> + intel_vrr_max_guardband(crtc_state));
>
> + if (DISPLAY_VER(display) < 13)
> crtc_state->vrr.pipeline_full =
> intel_vrr_guardband_to_pipeline_full(crtc_state,
>
> crtc_state->vrr.guardband);
> - }
> }
>
> static u32 trans_vrr_ctl(const struct intel_crtc_state *crtc_state)
> --
> 2.45.2
--
Ville Syrjälä
Intel
