Commit 1c3c1dc6 authored Apr 23, 2018 by Mika Kuoppala

drm/i915: Add compiler barrier to wait_for



We need to be careful to not let compiler evaluate
the expiration and the operation on it's terms.

Document and enforce that COND will be evaluated
before checking timeout expiration.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423113754.28424-2-mika.kuoppala@linux.intel.com

parent 3085982c

drivers/gpu/drm/i915/intel_drv.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -56,6 +56,8 @@
		for (;;) { \
		const bool expired__ = ktime_after(ktime_get_raw(), end__); \
		OP; \
		/* Guarantee COND check prior to timeout */ \
		barrier(); \
		if (COND) { \
		ret__ = 0; \
		break; \
		@@ -96,6 +98,8 @@
		u64 now = local_clock(); \
		if (!(ATOMIC)) \
		preempt_enable(); \
		/* Guarantee COND check prior to timeout */ \
		barrier(); \
		if (COND) { \
		ret = 0; \
		break; \