[Intel-gfx] [PATCH 6/6] drm/i915: Do not lie about atomic wait granularity

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Currently the wait_for_atomic_us only allows for a millisecond
granularity which is not nice towards callers requesting small
micro-second waits.

Re-implement it so micro-second granularity is really supported
and not just in the name of the macro.

v2:
  * Warn when used from non-atomic context (if possible).
  * Warn on too long atomic waits.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_drv.h | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 779d17a9fcce..af6c1539106f 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -63,11 +63,32 @@
 	ret__;								\
 })
 
+#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT)
+  #define _WAIT_FOR_ATOMIC_CHECK WARN_ON_ONCE(!in_atomic())
+#else
+  #define _WAIT_FOR_ATOMIC_CHECK do { } while(0)
+#endif
+
+#define _wait_for_atomic(COND, US) ({ \
+	unsigned long end__; \
+	int ret__ = 0; \
+	_WAIT_FOR_ATOMIC_CHECK; \
+	BUILD_BUG_ON((US) > 50000); \
+	end__ = (local_clock() >> 10) + (US) + 1; \
+	while (!(COND)) { \
+		if (time_after((unsigned long)(local_clock() >> 10), end__)) { \
+			ret__ = -ETIMEDOUT; \
+			break; \
+		} \
+		cpu_relax(); \
+	} \
+	ret__; \
+})
+
 #define wait_for(COND, MS) _wait_for(COND, (MS) * 1000, 1000)
 #define wait_for_us(COND, US) _wait_for(COND, US, 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 wait_for_atomic(COND, MS) _wait_for_atomic(COND, (MS) * 1000)
+#define wait_for_atomic_us(COND, US) _wait_for_atomic((COND), (US))
 
 #define KHz(x) (1000 * (x))
 #define MHz(x) KHz(1000 * (x))
-- 
1.9.1