On Fri, Dec 02, 2022 at 03:44:10PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> We are miscalculating both the guardband value, and the resulting
> vblank exit length on adl+. This means that our start of vblank
> (double buffered register latch point) is incorrect, and we also
> think that it's not where it actually is (hence vblank evasion/etc.
> may not work properly). Fix up the calculations to match the real
> hardware behaviour (as reverse engineered by intel_display_poller).
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_vrr.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 6655dd2c1684..753e7b211708 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> @@ -78,10 +78,10 @@ static int intel_vrr_vblank_exit_length(const struct intel_crtc_state *crtc_stat
> struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> struct drm_i915_private *i915 = to_i915(crtc->base.dev);
>
> - /* The hw imposes the extra scanline before frame start */
> if (DISPLAY_VER(i915) >= 13)
> - return crtc_state->vrr.guardband + crtc_state->framestart_delay + 1;
> + return crtc_state->vrr.guardband;
This makes sense since with guardband, there is no framestart delay
> else
> + /* The hw imposes the extra scanline before frame start */
> return crtc_state->vrr.pipeline_full + crtc_state->framestart_delay + 1;
> }
>
> @@ -151,7 +151,7 @@ intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
> * number of scan lines. Assuming 0 for no DSB.
> */
> crtc_state->vrr.guardband =
> - crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay;
> + crtc_state->vrr.vmin + 1 - adjusted_mode->crtc_vdisplay;
Why are we adding + 1 here? The bspec says guardband should be :
Guardband = Vmin - Vactive - Window2 where in our case Window2 = 0
If we need that + 1 to get this working, then perhaps we need to update
Bspec?
I kind of want to see if this is still breaking if we dont have that +
1?
Manasi
> } else {
> crtc_state->vrr.pipeline_full =
> min(255, crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay -
> --
> 2.37.4
>
