On Fri, 01 Mar 2019 06:03:41 PST (-0800), Will Deacon wrote:
In a bid to kill off explicit mmiowb() usage in driver code, hook up
the asm-generic mmiowb() tracking code for riscv, so that an mmiowb()
is automatically issued from spin_unlock() if an I/O write was performed
in the critical section.
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/Kbuild | 1 -
arch/riscv/include/asm/io.h | 15 ++-------------
arch/riscv/include/asm/mmiowb.h | 14 ++++++++++++++
4 files changed, 17 insertions(+), 14 deletions(-)
create mode 100644 arch/riscv/include/asm/mmiowb.h
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 515fc3cc9687..08f4415203c5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -49,6 +49,7 @@ config RISCV
select RISCV_TIMER
select GENERIC_IRQ_MULTI_HANDLER
select ARCH_HAS_PTE_SPECIAL
+ select ARCH_HAS_MMIOWB
config MMU
def_bool y
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 221cd2ec78a4..cccd12cf27d4 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -21,7 +21,6 @@ generic-y += kvm_para.h
generic-y += local.h
generic-y += local64.h
generic-y += mm-arch-hooks.h
-generic-y += mmiowb.h
generic-y += mutex.h
generic-y += percpu.h
generic-y += preempt.h
diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
index 1d9c1376dc64..744fd92e77bc 100644
--- a/arch/riscv/include/asm/io.h
+++ b/arch/riscv/include/asm/io.h
@@ -20,6 +20,7 @@
#define _ASM_RISCV_IO_H
#include <linux/types.h>
+#include <asm/mmiowb.h>
extern void __iomem *ioremap(phys_addr_t offset, unsigned long size);
@@ -100,18 +101,6 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
#endif
/*
- * FIXME: I'm flip-flopping on whether or not we should keep this or enforce
- * the ordering with I/O on spinlocks like PowerPC does. The worry is that
- * drivers won't get this correct, but I also don't want to introduce a fence
- * into the lock code that otherwise only uses AMOs (and is essentially defined
- * by the ISA to be correct). For now I'm leaving this here: "o,w" is
- * sufficient to ensure that all writes to the device have completed before the
- * write to the spinlock is allowed to commit. I surmised this from reading
- * "ACQUIRES VS I/O ACCESSES" in memory-barriers.txt.
- */
-#define mmiowb() __asm__ __volatile__ ("fence o,w" : : : "memory");
-
-/*
* Unordered I/O memory access primitives. These are even more relaxed than
* the relaxed versions, as they don't even order accesses between successive
* operations to the I/O regions.
@@ -165,7 +154,7 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
#define __io_br() do {} while (0)
#define __io_ar(v) __asm__ __volatile__ ("fence i,r" : : : "memory");
#define __io_bw() __asm__ __volatile__ ("fence w,o" : : : "memory");
-#define __io_aw() do {} while (0)
+#define __io_aw() mmiowb_set_pending()
#define readb(c) ({ u8 __v; __io_br(); __v = readb_cpu(c); __io_ar(__v); __v; })
#define readw(c) ({ u16 __v; __io_br(); __v = readw_cpu(c); __io_ar(__v); __v; })
diff --git a/arch/riscv/include/asm/mmiowb.h b/arch/riscv/include/asm/mmiowb.h
new file mode 100644
index 000000000000..5d7e3a2b4e3b
--- /dev/null
+++ b/arch/riscv/include/asm/mmiowb.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_RISCV_MMIOWB_H
+#define _ASM_RISCV_MMIOWB_H
+
+/*
+ * "o,w" is sufficient to ensure that all writes to the device have completed
+ * before the write to the spinlock is allowed to commit.
+ */
+#define mmiowb() __asm__ __volatile__ ("fence o,w" : : : "memory");
+
+#include <asm-generic/mmiowb.h>
+
+#endif /* ASM_RISCV_MMIOWB_H */
Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxx>
Thanks for doing this, that comment was one of the more headache-incuding
FIXMEs in our port. I think it's better to keep __io_aw next to the others:
even if it's the same as the generic implementation, it's easier to reason
about this way.
