[Intel-gfx] [PATCH 3/7] drm/i915: Spin opportunistically in wait_for

[Mika Kuoppala]

Usually the condition we are after appears within very short time.
Spin few times before going into sleep. With this approximately
half of the wait_for in init path will take the fast path without
sleeping.

Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 488141929a7a..c225605c727c 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -39,7 +39,7 @@
 #include <drm/drm_atomic.h>
 
 /**
- * _wait_for_ms - magic (register) wait macro
+ * __wait_for_ms - magic (register) wait macro
  *
  * Does the right thing for modeset paths when run under kdgb or similar atomic
  * contexts. Note that it's important that we check the condition again after
@@ -50,17 +50,22 @@
  * drm_can_sleep() can be removed and in_atomic()/!in_atomic() asserts
  * added.
  */
-#define _wait_for_ms(COND, TIMEOUT_MS, SLEEP_US) ({ \
+#define __wait_for_ms(COND, TIMEOUT_MS, SLEEP_US, SPIN_COUNT) ({	\
 	const unsigned long timeout__ =					\
 		jiffies + msecs_to_jiffies(TIMEOUT_MS) + 1;		\
+	unsigned int c__ = 0;						\
 	int ret__ = 0;							\
+									\
 	while (!(COND)) {						\
 		if (time_after(jiffies, timeout__)) {			\
 			if (!(COND))					\
 				ret__ = -ETIMEDOUT;			\
 			break;						\
 		}							\
-		if ((SLEEP_US) && drm_can_sleep()) {			\
+									\
+		if (++c__ > (SPIN_COUNT) &&				\
+		    (SLEEP_US) &&					\
+		    drm_can_sleep()) {					\
 			usleep_range((SLEEP_US), (SLEEP_US) * 2);	\
 		} else {						\
 			cpu_relax();					\
@@ -69,7 +74,8 @@
 	ret__;								\
 })
 
-#define wait_for(COND, MS)	 _wait_for_ms((COND), (MS), 1 * USEC_PER_MSEC)
+#define wait_for(COND, MS)  __wait_for_ms((COND), (MS), 1 * USEC_PER_MSEC, 5)
+#define _wait_for_ms(COND, MS, US)  __wait_for_ms((COND), (MS), (US), 5)
 
 /* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
 #if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT)
-- 
2.5.0