From 435db526a68b6454a882eae7a3768c516d4b540e Mon Sep 17 00:00:00 2001
From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Tue, 4 Apr 2023 20:54:30 +0300
Subject: [PATCH] drm/i915: Evade transcoder's vblank when doing seamless M/N
 changes
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The transcoder M/N values are double buffered on the transcoder's
undelayed vblank. So when doing seamless M/N fastsets we need to
evade also that.

Note that currently the pipe's delayed vblank == transcoder's
undelayed vblank, so this is still a nop change. But in the
future when we may have to delay the pipe's vblank to create
a register programming window ("window2") for the DSB.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230404175431.23064-2-ville.syrjala@linux.intel.com
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com
---
 drivers/gpu/drm/i915/display/intel_crtc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
index b92df8814f247..df7d05f1e14b3 100644
--- a/drivers/gpu/drm/i915/display/intel_crtc.c
+++ b/drivers/gpu/drm/i915/display/intel_crtc.c
@@ -510,6 +510,13 @@ void intel_pipe_update_start(struct intel_crtc_state *new_crtc_state)
 						      VBLANK_EVASION_TIME_US);
 	max = vblank_start - 1;
 
+	/*
+	 * M/N is double buffered on the transcoder's undelayed vblank,
+	 * so with seamless M/N we must evade both vblanks.
+	 */
+	if (new_crtc_state->seamless_m_n && intel_crtc_needs_fastset(new_crtc_state))
+		min -= adjusted_mode->crtc_vblank_start - adjusted_mode->crtc_vdisplay;
+
 	if (min <= 0 || max <= 0)
 		goto irq_disable;
 
-- 
2.30.2