drm/i915: Evade transcoder's vblank when doing seamless M/N changes

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

diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
index b92df88..df7d05f 100644 (file)
--- 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;