drm/i915/vrr: Make registers latch in a consitent place on icl/tgl

Account for the framestart delay when calculating the "pipeline full"
value for icl/tgl vrr. This puts the start of vblank (ie. where the
double bufferd registers get latched) to a consistent place regardless
of what framestart delay value is used. framestart delay does not
change where start of vblank occurs in non-vrr mode and I can't see
any reason why we'd want different behaviour in vrr mode.

Currently framestart delay is always set to 1, and the hardcoded 4
scanlines in the code means we're currently delaying the start of
vblank by three extra lines. And with framestart delay set to 4 we'd
have no extra delay.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221202134412.21943-2-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index 7b1357e..6655dd2 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -153,18 +153,9 @@ intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
                crtc_state->vrr.guardband =
                        crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay;
        } else {
-               /*
-                * FIXME: s/4/framestart_delay/ to get consistent
-                * earliest/latest points for register latching regardless
-                * of the framestart_delay used?
-                *
-                * FIXME: this really needs the extra scanline to provide consistent
-                * behaviour for all framestart_delay values. Otherwise with
-                * framestart_delay==4 we will end up extending the min vblank by
-                * one extra line.
-                */
                crtc_state->vrr.pipeline_full =
-                       min(255, crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay - 4 - 1);
+                       min(255, crtc_state->vrr.vmin - adjusted_mode->crtc_vdisplay -
+                           crtc_state->framestart_delay - 1);
        }
 
        crtc_state->mode_flags |= I915_MODE_FLAG_VRR;