drm/i915: Use msleep instead of mdelay during wait_vblank_off

Avoid a potentially long busy-wait if we not in the process of
atomically switching to the kdb console.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -1034,16 +1034,17 @@ void intel_wait_for_vblank_off(struct drm_device *dev, int pipe)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	int pipedsl_reg = (pipe == 0 ? PIPEADSL : PIPEBDSL);
 	unsigned long timeout = jiffies + msecs_to_jiffies(100);
-	u32 last_line;
+	u32 last_line, line;
 
 	/* Wait for the display line to settle */
+	line = I915_READ(pipedsl_reg) & DSL_LINEMASK;
 	do {
-		last_line = I915_READ(pipedsl_reg) & DSL_LINEMASK;
-		mdelay(5);
-	} while (((I915_READ(pipedsl_reg) & DSL_LINEMASK) != last_line) &&
-		 time_after(timeout, jiffies));
+		last_line = line;
+		MSLEEP(5);
+		line = I915_READ(pipedsl_reg) & DSL_LINEMASK;
+	} while (line != last_line && time_after(timeout, jiffies));
 
-	if (time_after(jiffies, timeout))
+	if (line != last_line)
 		DRM_DEBUG_KMS("vblank wait timed out\n");
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -49,6 +49,13 @@
 #define wait_for(COND, MS) _wait_for(COND, MS, 1)
 #define wait_for_atomic(COND, MS) _wait_for(COND, MS, 0)
 
+#define MSLEEP(x) do { \
+	if (in_dbg_master()) \
+	       	mdelay(x); \
+	else \
+		msleep(x); \
+} while(0)
+
 #define KHz(x) (1000*x)
 #define MHz(x) KHz(1000*x)