[Intel-gfx] [PATCH] drm/i915: Only expand COND once in wait_for()

[Chris Wilson]

I was looking at some wait_for() timeouts on a slow system, with lots of
debug enabled (KASAN, lockdep, mmio_debug). Thinking that we were
mishandling the timeout, I tried to ensure that we loop at least once
after first testing COND. However, the double test of COND either side
of the timeout check makes that unlikely. But we can do an equivalent
loop, that keeps the COND check after testing for timeout (required so
that we are not preempted between testing COND and then testing for a
timeout) without expanding COND twice.

The advantage of only expanding COND once is a dramatic reduction in
code size:

   text	   data	    bss	    dec	    hex
1308733	   5184	   1152	1315069	 1410fd	before
1305341	   5184	   1152	1311677	 1403bd	after

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/intel_drv.h | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index cb99a2540863..597899d71df9 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -52,13 +52,16 @@
  */
 #define _wait_for(COND, US, W) ({ \
 	unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;	\
-	int ret__ = 0;							\
-	while (!(COND)) {						\
-		if (time_after(jiffies, timeout__)) {			\
-			if (!(COND))					\
-				ret__ = -ETIMEDOUT;			\
+	int ret__;							\
+	for (;;) {							\
+		if (time_after(jiffies, timeout__))			\
+			ret__ = -ETIMEDOUT;				\
+		if (COND) {						\
+			ret__ = 0;					\
 			break;						\
 		}							\
+		if (ret__)						\
+			break;						\
 		if ((W) && drm_can_sleep()) {				\
 			usleep_range((W), (W)*2);			\
 		} else {						\
-- 
2.9.3