[PATCH 2/2] drm/i915: Use atomic waits for short non-atomic ones

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

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

usleep_range is not recommended for waits shorten than 10us.

Make the wait_for_us use the atomic variant for such waits.

To do so we need to disable the !in_atomic warning for such uses
and also disable preemption since the macro is written in a way
to only be safe to be used in atomic context (local_clock() and
no second COND check after the timeout).

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 3156d8df7921..e21bf6e6f119 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -69,20 +69,21 @@
 })
 
 #define wait_for(COND, MS)	  	_wait_for((COND), (MS) * 1000, 1000)
-#define wait_for_us(COND, US)	  	_wait_for((COND), (US), 1)
 
 /* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
 #if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT)
-# define _WAIT_FOR_ATOMIC_CHECK WARN_ON_ONCE(!in_atomic())
+# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
 #else
-# define _WAIT_FOR_ATOMIC_CHECK do { } while (0)
+# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)
 #endif
 
-#define _wait_for_atomic(COND, US) ({ \
+#define _wait_for_atomic(COND, US, ATOMIC) ({ \
 	unsigned long end__; \
 	int ret__ = 0; \
-	_WAIT_FOR_ATOMIC_CHECK; \
-	BUILD_BUG_ON((US) > 50000); \
+	_WAIT_FOR_ATOMIC_CHECK(ATOMIC); \
+	BUILD_BUG_ON((ATOMIC) && (US) > 50000); \
+	if (!(ATOMIC)) \
+		preempt_disable(); \
 	end__ = (local_clock() >> 10) + (US) + 1; \
 	while (!(COND)) { \
 		if (time_after((unsigned long)(local_clock() >> 10), end__)) { \
@@ -97,11 +98,23 @@
 		} \
 		cpu_relax(); \
 	} \
+	if (!(ATOMIC)) \
+		preempt_enable(); \
 	ret__; \
 })
 
-#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 wait_for_us(COND, US) \
+({ \
+	int ret__; \
+	if ((US) > 10) \
+		ret__ = _wait_for((COND), (US), 10); \
+	else \
+		ret__ = _wait_for_atomic((COND), (US), 0); \
+	ret__; \
+})
+
+#define wait_for_atomic(COND, MS)	_wait_for_atomic((COND), (MS) * 1000, 1)
+#define wait_for_atomic_us(COND, US)	_wait_for_atomic((COND), (US), 1)
 
 #define KHz(x) (1000 * (x))
 #define MHz(x) KHz(1000 * (x))
-- 
1.9.1

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