drm/i915: remove wait_for_vblank argument form intel_enable_pipe

Add a nice comment explaining why we shouldn't wait for a vblank on
all cases, wait based on the HW gen, and add a comment saying we
should probably skip that wait on some of the previous HW gens.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -1747,12 +1747,11 @@ static void lpt_disable_pch_transcoder(struct drm_i915_private *dev_priv)
 /**
  * intel_enable_pipe - enable a pipe, asserting requirements
  * @crtc: crtc responsible for the pipe
- * @wait_for_vblank: whether we should for a vblank or not after enabling it
  *
  * Enable @crtc's pipe, making sure that various hardware specific requirements
  * are met, if applicable, e.g. PLL enabled, LVDS pairs enabled, etc.
  */
-static void intel_enable_pipe(struct intel_crtc *crtc, bool wait_for_vblank)
+static void intel_enable_pipe(struct intel_crtc *crtc)
 {
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -1799,7 +1798,15 @@ static void intel_enable_pipe(struct intel_crtc *crtc, bool wait_for_vblank)
 
 	I915_WRITE(reg, val | PIPECONF_ENABLE);
 	POSTING_READ(reg);
-	if (wait_for_vblank)
+
+	/*
+	 * There's no guarantee the pipe will really start running now. It
+	 * depends on the Gen, the output type and the relative order between
+	 * pipe and plane enabling. Avoid waiting on HSW+ since it's not
+	 * necessary.
+	 * TODO: audit the previous gens.
+	 */
+	if (INTEL_INFO(dev)->gen <= 7 && !IS_HASWELL(dev))
 		intel_wait_for_vblank(dev_priv->dev, pipe);
 }
 
@@ -3596,7 +3603,7 @@ static void ironlake_crtc_enable(struct drm_crtc *crtc)
 	intel_crtc_load_lut(crtc);
 
 	intel_update_watermarks(crtc);
-	intel_enable_pipe(intel_crtc, true);
+	intel_enable_pipe(intel_crtc);
 	intel_enable_primary_plane(dev_priv, plane, pipe);
 	intel_enable_planes(crtc);
 	intel_crtc_update_cursor(crtc, true);
@@ -3741,7 +3748,7 @@ static void haswell_crtc_enable(struct drm_crtc *crtc)
 	intel_ddi_enable_transcoder_func(crtc);
 
 	intel_update_watermarks(crtc);
-	intel_enable_pipe(intel_crtc, false);
+	intel_enable_pipe(intel_crtc);
 
 	if (intel_crtc->config.has_pch_encoder)
 		lpt_pch_enable(crtc);
@@ -4166,7 +4173,7 @@ static void valleyview_crtc_enable(struct drm_crtc *crtc)
 	intel_crtc_load_lut(crtc);
 
 	intel_update_watermarks(crtc);
-	intel_enable_pipe(intel_crtc, true);
+	intel_enable_pipe(intel_crtc);
 	intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
 	intel_enable_primary_plane(dev_priv, plane, pipe);
 	intel_enable_planes(crtc);
@@ -4205,7 +4212,7 @@ static void i9xx_crtc_enable(struct drm_crtc *crtc)
 	intel_crtc_load_lut(crtc);
 
 	intel_update_watermarks(crtc);
-	intel_enable_pipe(intel_crtc, true);
+	intel_enable_pipe(intel_crtc);
 	intel_set_cpu_fifo_underrun_reporting(dev, pipe, true);
 	intel_enable_primary_plane(dev_priv, plane, pipe);
 	intel_enable_planes(crtc);