[PATCH] RFC drm/i915: Only acquire vblank-irq when waiting for vblank evade

* [PATCH] RFC drm/i915: Only acquire vblank-irq when waiting for vblank evade
@ 2018-02-12 21:37 Chris Wilson
  2018-02-12 22:16 ` ✗ Fi.CI.BAT: warning for " Patchwork
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Chris Wilson @ 2018-02-12 21:37 UTC (permalink / raw)
  To: intel-gfx

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_sprite.c | 65 ++++++++++++++++++++++---------------
 1 file changed, 38 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index e098e4b2c85c..dd8c1f24980f 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -74,6 +74,14 @@ int intel_usecs_to_scanlines(const struct drm_display_mode *adjusted_mode,
 #define VBLANK_EVASION_TIME_US 100
 #endif
 
+static inline bool scanline_in_vblank(struct intel_crtc *crtc,
+				      int min, int max,
+				      int *scanline)
+{
+	*scanline = intel_get_crtc_scanline(crtc);
+	return *scanline < min && *scanline > max;
+}
+
 /**
  * intel_pipe_update_start() - start update of a set of display registers
  * @new_crtc_state: the new crtc state
@@ -91,12 +99,9 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 	struct intel_crtc *crtc = to_intel_crtc(new_crtc_state->base.crtc);
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	const struct drm_display_mode *adjusted_mode = &new_crtc_state->base.adjusted_mode;
-	long timeout = msecs_to_jiffies_timeout(1);
 	int scanline, min, max, vblank_start;
-	wait_queue_head_t *wq = drm_crtc_vblank_waitqueue(&crtc->base);
 	bool need_vlv_dsi_wa = (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) &&
 		intel_crtc_has_type(new_crtc_state, INTEL_OUTPUT_DSI);
-	DEFINE_WAIT(wait);
 
 	vblank_start = adjusted_mode->crtc_vblank_start;
 	if (adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE)
@@ -112,41 +117,46 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 	if (min <= 0 || max <= 0)
 		return;
 
-	if (WARN_ON(drm_crtc_vblank_get(&crtc->base)))
-		return;
-
 	crtc->debug.min_vbl = min;
 	crtc->debug.max_vbl = max;
 	trace_i915_pipe_update_start(crtc);
 
-	for (;;) {
-		/*
-		 * prepare_to_wait() has a memory barrier, which guarantees
-		 * other CPUs can see the task state update by the time we
-		 * read the scanline.
-		 */
-		prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
+	if (!scanline_in_vblank(crtc, min, max, &scanline)) {
+		wait_queue_head_t *wq = drm_crtc_vblank_waitqueue(&crtc->base);
+		long timeout = msecs_to_jiffies_timeout(1);
+		DEFINE_WAIT(wait);
 
-		scanline = intel_get_crtc_scanline(crtc);
-		if (scanline < min || scanline > max)
-			break;
+		if (WARN_ON(drm_crtc_vblank_get(&crtc->base)))
+			goto skip_evade;
 
-		if (timeout <= 0) {
-			DRM_ERROR("Potential atomic update failure on pipe %c\n",
-				  pipe_name(crtc->pipe));
-			break;
-		}
+		for (;;) {
+			/*
+			 * prepare_to_wait() has a memory barrier, which
+			 * guarantees other CPUs can see the task state update
+			 * by the time we read the scanline.
+			 */
+			prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
 
-		local_irq_enable();
+			if (scanline_in_vblank(crtc, min, max, &scanline))
+				break;
 
-		timeout = schedule_timeout(timeout);
+			if (timeout <= 0) {
+				DRM_ERROR("Potential atomic update failure on pipe %c\n",
+					  pipe_name(crtc->pipe));
+				break;
+			}
 
-		local_irq_disable();
-	}
+			local_irq_enable();
 
-	finish_wait(wq, &wait);
+			timeout = schedule_timeout(timeout);
 
-	drm_crtc_vblank_put(&crtc->base);
+			local_irq_disable();
+		}
+
+		finish_wait(wq, &wait);
+
+		drm_crtc_vblank_put(&crtc->base);
+	}
 
 	/*
 	 * On VLV/CHV DSI the scanline counter would appear to
@@ -166,6 +176,7 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 	while (need_vlv_dsi_wa && scanline == vblank_start)
 		scanline = intel_get_crtc_scanline(crtc);
 
+skip_evade:
 	crtc->debug.scanline_start = scanline;
 	crtc->debug.start_vbl_time = ktime_get();
 	crtc->debug.start_vbl_count = intel_crtc_get_vblank_counter(crtc);
-- 
2.16.1

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