[PATCH 09/20] sh/mmiowb: Add unconditional mmiowb() to arch_spin_unlock()

Will Deacon
2019-03-01T14:04:37Z

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 sh. 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.

Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/sh/include/asm/Kbuild | 1 -
arch/sh/include/asm/io.h | 3 ---
arch/sh/include/asm/mmiowb.h | 12 ++++++++++++
arch/sh/include/asm/spinlock-llsc.h | 2 ++
4 files changed, 14 insertions(+), 4 deletions(-)
create mode 100644 arch/sh/include/asm/mmiowb.h

diff --git a/arch/sh/include/asm/Kbuild b/arch/sh/include/asm/Kbuild
index e3f6926c4b86..a6ef3fee5f85 100644
--- a/arch/sh/include/asm/Kbuild
+++ b/arch/sh/include/asm/Kbuild
@@ -13,7 +13,6 @@ generic-y += local.h
generic-y += local64.h
generic-y += mcs_spinlock.h
generic-y += mm-arch-hooks.h
-generic-y += mmiowb.h
generic-y += parport.h
generic-y += percpu.h
generic-y += preempt.h
diff --git a/arch/sh/include/asm/io.h b/arch/sh/include/asm/io.h
index 4f7f235f15f8..c28e37a344ad 100644
--- a/arch/sh/include/asm/io.h
+++ b/arch/sh/include/asm/io.h
@@ -229,9 +229,6 @@ __BUILD_IOPORT_STRING(q, u64)

#define IO_SPACE_LIMIT 0xffffffff

-/* synco on SH-4A, otherwise a nop */
-#define mmiowb() wmb()
-
/* We really want to try and get these to memcpy etc */
void memcpy_fromio(void *, const volatile void __iomem *, unsigned long);
void memcpy_toio(volatile void __iomem *, const void *, unsigned long);
diff --git a/arch/sh/include/asm/mmiowb.h b/arch/sh/include/asm/mmiowb.h
new file mode 100644
index 000000000000..535d59735f1d
--- /dev/null
+++ b/arch/sh/include/asm/mmiowb.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_SH_MMIOWB_H
+#define __ASM_SH_MMIOWB_H
+
+#include <asm/barrier.h>
+
+/* synco on SH-4A, otherwise a nop */
+#define mmiowb() wmb()
+
+#include <asm-generic/mmiowb.h>
+
+#endif /* __ASM_SH_MMIOWB_H */
diff --git a/arch/sh/include/asm/spinlock-llsc.h b/arch/sh/include/asm/spinlock-llsc.h
index 786ee0fde3b0..7fd929cd2e7a 100644
--- a/arch/sh/include/asm/spinlock-llsc.h
+++ b/arch/sh/include/asm/spinlock-llsc.h
@@ -47,6 +47,8 @@ static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
unsigned long tmp;

+ /* This could be optimised with ARCH_HAS_MMIOWB */
+ mmiowb();
__asm__ __volatile__ (
"mov #1, %0 ! arch_spin_unlock \n\t"
"mov.l %0, @%1 \n\t"
--
2.11.0