drm/i915/vrr: Add extra vblank delay to estimates

On ICL/TGL the VRR hardware injects an extra scanline just after
vactive. This essentically behaves the same as an extra line of
vblank delay, except it only appears in this one specific spot.

Consider our DSB interrupt signalling scheme:
1. arm the update
2. wait for undelayed vblank (or rather safe window with VRR)
3. wait for enough usecs to get past the delayed vblank
4. signal interrupt to indicate that arming has latched

If step 2 waits for end of vactive step 3 needs to account for
the extra one scanline, or else we risk signalling the interrupt
before the delayed vblank has actually elapsed. So include the
extra scanline in our vblank delay estimates.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241210211007.5976-16-ville.syrjala@linux.intel.com
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index 1110f0e65e885f56f5261b8869f73b3bcb2cefe1..b5e30bfe17916d1bca25e0a1ac12a5300a59a3cc 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -75,12 +75,33 @@ intel_vrr_check_modeset(struct intel_atomic_state *state)
        }
 }
 
-int intel_vrr_vblank_delay(const struct intel_crtc_state *crtc_state)
+static int intel_vrr_real_vblank_delay(const struct intel_crtc_state *crtc_state)
 {
        return crtc_state->hw.adjusted_mode.crtc_vblank_start -
                crtc_state->hw.adjusted_mode.crtc_vdisplay;
 }
 
+static int intel_vrr_extra_vblank_delay(struct intel_display *display)
+{
+       /*
+        * On ICL/TGL VRR hardware inserts one extra scanline
+        * just after vactive, which pushes the vmin decision
+        * boundary ahead accordingly. We'll include the extra
+        * scanline in our vblank delay estimates to make sure
+        * that we never underestimate how long we have until
+        * the delayed vblank has passed.
+        */
+       return DISPLAY_VER(display) < 13 ? 1 : 0;
+}
+
+int intel_vrr_vblank_delay(const struct intel_crtc_state *crtc_state)
+{
+       struct intel_display *display = to_intel_display(crtc_state);
+
+       return intel_vrr_real_vblank_delay(crtc_state) +
+               intel_vrr_extra_vblank_delay(display);
+}
+
 static int intel_vrr_flipline_offset(struct intel_display *display)
 {
        /* ICL/TGL hardware imposes flipline>=vmin+1 */
@@ -130,7 +151,7 @@ int intel_vrr_vmin_vtotal(const struct intel_crtc_state *crtc_state)
                return intel_vrr_vmin_flipline(crtc_state);
        else
                return intel_vrr_vmin_flipline(crtc_state) +
-                       intel_vrr_vblank_delay(crtc_state);
+                       intel_vrr_real_vblank_delay(crtc_state);
 }
 
 int intel_vrr_vmax_vtotal(const struct intel_crtc_state *crtc_state)
@@ -141,7 +162,7 @@ int intel_vrr_vmax_vtotal(const struct intel_crtc_state *crtc_state)
                return crtc_state->vrr.vmax;
        else
                return crtc_state->vrr.vmax +
-                       intel_vrr_vblank_delay(crtc_state);
+                       intel_vrr_real_vblank_delay(crtc_state);
 }
 
 int intel_vrr_vmin_vblank_start(const struct intel_crtc_state *crtc_state)
@@ -309,9 +330,9 @@ void intel_vrr_compute_config_late(struct intel_crtc_state *crtc_state)
                 * vmin/vmax/flipline also need to be adjusted by
                 * the vblank delay to maintain correct vtotals.
                 */
-               crtc_state->vrr.vmin -= intel_vrr_vblank_delay(crtc_state);
-               crtc_state->vrr.vmax -= intel_vrr_vblank_delay(crtc_state);
-               crtc_state->vrr.flipline -= intel_vrr_vblank_delay(crtc_state);
+               crtc_state->vrr.vmin -= intel_vrr_real_vblank_delay(crtc_state);
+               crtc_state->vrr.vmax -= intel_vrr_real_vblank_delay(crtc_state);
+               crtc_state->vrr.flipline -= intel_vrr_real_vblank_delay(crtc_state);
        }
 }