[Intel-gfx] [PATCH v4] drm/i915: use hrtimer in wait for vblank

[Arun R Murthy]

In wait for vblank use usleep_range, which will use hrtimers instead of
msleep. Using msleep(1~20) there are more chances of sleeping for 20ms.
Using usleep_range uses hrtimers and hence are precise, worst case will
trigger an interrupt at the higher/max timeout.

As per kernel document "Documentation/timers/timers-howto.txt" sleeping
for 10us to 20ms its recomended to use usleep_range.

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 44067bc..29a8664 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -52,7 +52,10 @@
 			break;						\
 		}							\
 		if (W && drm_can_sleep())  {				\
-			msleep(W);					\
+			if (W > 20)					\
+				msleep(W);				\
+			else						\
+				usleep_range(W * 1000, W * 2 * 1000);	\
 		} else {						\
 			cpu_relax();					\
 		}							\
-- 
1.7.9.5