Fix the CAS spinlock implementation
Make the spinlock implementation use ARMv8.1-LSE CAS instruction based
on a platform build option. The CAS-based implementation used to be
unconditionally selected for all ARM8.1+ platforms.
The previous CAS spinlock implementation had a bug wherein the spin_unlock()
implementation had an `sev` after `stlr` which is not sufficient. A dsb is
needed to ensure that the stlr completes prior to the sev. Having a dsb is
heavyweight and a better solution would be to use load exclusive semantics
to monitor the lock and wake up from wfe when a store happens to the lock.
The patch implements the same.
Change-Id: I5283ce4a889376e4cc01d1b9d09afa8229a2e522
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index b6f7655..b7fb173 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -234,3 +234,8 @@
endif
SANITIZE_UB := off
+
+# For ARMv8.1 (AArch64) platforms, enabling this option selects the spinlock
+# implementation variant using the ARMv8.1-LSE compare-and-swap instruction.
+# Default: disabled
+USE_SPINLOCK_CAS := 0