drm/i915: Add wait_for_us

This is for callers who want micro-second precision but are not
waiting from the atomic context.

v2:
  * Fix atomic waits. (Dave Gordon)
  * Use USEC_PER_SEC and USEC_PER_MSEC. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
index 0b42ada..b1413be 100644
--- a/drivers/gpu/drm/i915/intel_psr.c
+++ b/drivers/gpu/drm/i915/intel_psr.c
@@ -507,7 +507,8 @@
 
 		/* Wait till PSR is idle */
 		if (_wait_for((I915_READ(EDP_PSR_STATUS_CTL) &
-			       EDP_PSR_STATUS_STATE_MASK) == 0, 2000, 10))
+			       EDP_PSR_STATUS_STATE_MASK) == 0,
+			       2 * USEC_PER_SEC, 10 * USEC_PER_MSEC))
 			DRM_ERROR("Timed out waiting for PSR Idle State\n");
 
 		dev_priv->psr.active = false;