[Intel-gfx] [PATCH 2/3] drm/i915: Evade transcoder's vblank when doing seamless M/N changes

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

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.

Not 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 at linux.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 ed45a6934854..f3b836829296 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;
 
-- 
2.39.2