drm/i915: Use usleep_range() in wait_for()

msleep() can sleep for way too long, so switch wait_for() to use
usleep_range() instead. Following a totally unscientific method
I just picked the range as W-2W.

This cuts the i915 init time on my BSW to almost half:
- initcall i915_init+0x0/0xa8 [i915] returned 0 after 419977 usecs
+ initcall i915_init+0x0/0xa8 [i915] returned 0 after 238419 usecs

Note that I didn't perform any other benchmarks on this so far.

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 6f20f3a..d2a4de0 100644 (file)
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -56,8 +56,8 @@
                                ret__ = -ETIMEDOUT;                     \
                        break;                                          \
                }                                                       \
-               if (W && drm_can_sleep())  {                            \
-                       msleep(W);                                      \
+               if ((W) && drm_can_sleep()) {                           \
+                       usleep_range((W)*1000, (W)*2000);               \
                } else {                                                \
                        cpu_relax();                                    \
                }                                                       \