[PATCH v3 1/2] drm/i915/display: Ensure enough lines between delayed VBlank and VBlank

[Jouni Högander]

To deterministically capture the transition of the state machine going from
SRDOFFACK to IDLE, the delayed V. Blank should be at least one line after
the non-delayed V. Blank.

Ensure this by adding new interface into intel_psr to query number of lines
needed for vblank delay and call it from intel_crtc_vblank_delay.

v3: use existing intel_crtc_vblank_delay mechanism
v2: apply limits only when needed (VRR TG vs. Legacy TG)

Bspec: 69897
Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c |  2 +
 drivers/gpu/drm/i915/display/intel_psr.c     | 39 ++++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_psr.h     |  1 +
 3 files changed, 42 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 6bd55fd9dff85..a7b35fc13d7c8 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2422,6 +2422,8 @@ static int intel_crtc_vblank_delay(const struct intel_crtc_state *crtc_state)
 	if (intel_crtc_needs_wa_14015401596(crtc_state))
 		vblank_delay = max(vblank_delay, 1);
 
+	vblank_delay = max(vblank_delay, intel_psr_min_vblank_delay(crtc_state));
+
 	return vblank_delay;
 }
 
diff --git a/drivers/gpu/drm/i915/display/intel_psr.c b/drivers/gpu/drm/i915/display/intel_psr.c
index 127eec4272fda..1058134422bcf 100644
--- a/drivers/gpu/drm/i915/display/intel_psr.c
+++ b/drivers/gpu/drm/i915/display/intel_psr.c
@@ -2385,6 +2385,45 @@ void intel_psr_trigger_frame_change_event(struct intel_dsb *dsb,
 				   CURSURFLIVE(display, crtc->pipe), 0);
 }
 
+/**
+ * intel_psr_min_vblank_delay - Minimum vblank delay needed by PSR
+ * @crtc_state: the crtc state
+ *
+ * Return minimum vblank delay needed by PSR.
+ */
+int intel_psr_min_vblank_delay(const struct intel_crtc_state *crtc_state)
+{
+	struct intel_display *display = to_intel_display(crtc_state);
+
+	if (!crtc_state->has_psr || DISPLAY_VER(display) < 20)
+		return 0;
+
+	/*
+	 * Comment on SRD_STATUS register in Bspec for LunarLake and onwards:
+	 *
+	 * To deterministically capture the transition of the state machine
+	 * going from SRDOFFACK to IDLE, the delayed V. Blank should be at least
+	 * one line after the non-delayed V. Blank.
+	 *
+	 * Legacy TG: TRANS_SET_CONTEXT_LATENCY > 0
+	 * VRR TG: TRANS_VRR_CTL[ VRR Guardband ] < (TRANS_VRR_VMAX[ VRR Vmax ]
+	 * - TRANS_VTOTAL[ Vertical Active ])
+	 *
+	 * SRD_STATUS is used only by PSR1 on PantherLake.
+	 * SRD_STATUS is used by PSR1 and Panel Replay DP on LunarLake.
+	 */
+
+	if (DISPLAY_VER(display) >= 30 && (crtc_state->has_panel_replay ||
+					   crtc_state->has_sel_update))
+		return 0;
+	else if (DISPLAY_VER(display) < 30 && (crtc_state->has_sel_update ||
+					       intel_crtc_has_type(crtc_state,
+								   INTEL_OUTPUT_EDP)))
+		return 0;
+	else
+		return 1;
+}
+
 static u32 man_trk_ctl_enable_bit_get(struct intel_display *display)
 {
 	return display->platform.alderlake_p || DISPLAY_VER(display) >= 14 ? 0 :
diff --git a/drivers/gpu/drm/i915/display/intel_psr.h b/drivers/gpu/drm/i915/display/intel_psr.h
index c61384bb7382a..3838f01d1619c 100644
--- a/drivers/gpu/drm/i915/display/intel_psr.h
+++ b/drivers/gpu/drm/i915/display/intel_psr.h
@@ -73,6 +73,7 @@ void intel_psr_unlock(const struct intel_crtc_state *crtc_state);
 void intel_psr_trigger_frame_change_event(struct intel_dsb *dsb,
 					  struct intel_atomic_state *state,
 					  struct intel_crtc *crtc);
+int intel_psr_min_vblank_delay(const struct intel_crtc_state *crtc_state);
 void intel_psr_connector_debugfs_add(struct intel_connector *connector);
 void intel_psr_debugfs_register(struct intel_display *display);
 
-- 
2.43.0