ia64/mmiowb: Add unconditional mmiowb() to arch_spin_unlock()

The mmiowb() macro is horribly difficult to use and drivers will continue
to work most of the time if they omit a call when it is required.

Rather than rely on driver authors getting this right, push mmiowb() into
arch_spin_unlock() for ia64. If this is deemed to be a performance issue,
a subsequent optimisation could make use of ARCH_HAS_MMIOWB to elide
the barrier in cases where no I/O writes were performed inside the
critical section.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/arch/ia64/include/asm/mmiowb.h b/arch/ia64/include/asm/mmiowb.h
new file mode 100644
index 000000000000..297b85ac84a0
--- /dev/null
+++ b/arch/ia64/include/asm/mmiowb.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_IA64_MMIOWB_H
+#define _ASM_IA64_MMIOWB_H
+
+#include <asm/machvec.h>
+
+/**
+ * ___ia64_mmiowb - I/O write barrier
+ *
+ * Ensure ordering of I/O space writes.  This will make sure that writes
+ * following the barrier will arrive after all previous writes.  For most
+ * ia64 platforms, this is a simple 'mf.a' instruction.
+ */
+static inline void ___ia64_mmiowb(void)
+{
+	ia64_mfa();
+}
+
+#define __ia64_mmiowb	___ia64_mmiowb
+#define mmiowb()	platform_mmiowb()
+
+#include <asm-generic/mmiowb.h>
+
+#endif	/* _ASM_IA64_MMIOWB_H */