[Intel-gfx] [PATCH 12/12] drm/i915: Suppress spurious underruns on gen2

[Ville Syrjala]

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

Often we seem to detect an underrun right after modeset on gen2.
It seems to be a spurious detection (potentially the pipe is still
in a wonky state when we enable the planes). An extra vblank wait
seems to cure it.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index a0d1057d75ee..f330054e64c5 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -7517,6 +7517,10 @@ static void i9xx_crtc_enable(struct intel_atomic_state *state,
 	intel_crtc_vblank_on(new_crtc_state);
 
 	intel_encoders_enable(state, crtc);
+
+	/* prevents spurious underruns */
+	if (IS_GEN(dev_priv, 2))
+		intel_wait_for_vblank(dev_priv, pipe);
 }
 
 static void i9xx_pfit_disable(const struct intel_crtc_state *old_crtc_state)
-- 
2.24.1