drm/i915: fold wait_for_atomic_us into wait_for_atomic

Since

commit bcf9dcc1
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sun Jul 15 09:42:38 2012 +0100

    drm/i915: Workaround hang with BSD and forcewake on SandyBridge

and

commit 0cc2764c
Author: Ben Widawsky <ben@bwidawsk.net>
Date:   Sat Sep 1 22:59:48 2012 -0700

    drm/i915: use cpu_relax() in wait_for_atomic

these two macros are essentially the same, so unify them. We keep the
_us version since it's a nice documentation for smaller timeouts.

v2: Fixup time unit conversion, _wait_for takes ms (Ville).

Cc: Jack Winter <jbh@alchemy.lu>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -50,21 +50,10 @@
 	ret__;								\
 })
 
-#define wait_for_atomic_us(COND, US) ({ \
-	unsigned long timeout__ = jiffies + usecs_to_jiffies(US);	\
-	int ret__ = 0;							\
-	while (!(COND)) {						\
-		if (time_after(jiffies, timeout__)) {			\
-			ret__ = -ETIMEDOUT;				\
-			break;						\
-		}							\
-		cpu_relax();						\
-	}								\
-	ret__;								\
-})
-
 #define wait_for(COND, MS) _wait_for(COND, MS, 1)
 #define wait_for_atomic(COND, MS) _wait_for(COND, MS, 0)
+#define wait_for_atomic_us(COND, US) _wait_for((COND), \
+					       DIV_ROUND_UP((US), 1000), 0)
 
 #define KHz(x) (1000*x)
 #define MHz(x) KHz(1000*x)