[PATCH V10 03/19] riscv: qspinlock: errata: Add ERRATA_THEAD_WRITE_ONCE fixup

guoren
2023-08-02T16:48:40Z

The early version of T-Head C9xx cores has a store merge buffer
delay problem. The store merge buffer could improve the store queue
performance by merging multi-store requests, but when there are not
continued store requests, the prior single store request would be
waiting in the store queue for a long time. That would cause
significant problems for communication between multi-cores. This
problem was found on sg2042 & th1520 platforms with the qspinlock
lock torture test.

So appending a fence w.o could immediately flush the store merge
buffer and let other cores see the write result.

This will apply the WRITE_ONCE errata to handle the non-standard
behavior via appending a fence w.o instruction for WRITE_ONCE().

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
arch/riscv/Kconfig.errata | 19 +++++++++++++++++++
arch/riscv/errata/thead/errata.c | 20 ++++++++++++++++++++
arch/riscv/include/asm/errata_list.h | 13 -------------
arch/riscv/include/asm/rwonce.h | 24 ++++++++++++++++++++++++
arch/riscv/include/asm/vendorid_list.h | 14 ++++++++++++++
include/asm-generic/rwonce.h | 2 ++
6 files changed, 79 insertions(+), 13 deletions(-)
create mode 100644 arch/riscv/include/asm/rwonce.h

diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
index 0c8f4652cd82..4745a5c57e7c 100644
--- a/arch/riscv/Kconfig.errata
+++ b/arch/riscv/Kconfig.errata
@@ -77,4 +77,23 @@ config ERRATA_THEAD_PMU

If you don't know what to do here, say "Y".

+config ERRATA_THEAD_WRITE_ONCE
+ bool "Apply T-Head WRITE_ONCE errata"
+ depends on ERRATA_THEAD
+ default y
+ help
+ The early version of T-Head C9xx cores has a store merge buffer
+ delay problem. The store merge buffer could improve the store queue
+ performance by merging multi-store requests, but when there are no
+ continued store requests, the prior single store request would be
+ waiting in the store queue for a long time. That would cause
+ significant problems for communication between multi-cores. Appending
+ a fence w.o could immediately flush the store merge buffer and let
+ other cores see the write result.
+
+ This will apply the WRITE_ONCE errata to handle the non-standard
+ behavior via appending a fence w.o instruction for WRITE_ONCE().
+
+ If you don't know what to do here, say "Y".
+
endmenu # "CPU errata selection"
diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
index be84b14f0118..881729746d2e 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -69,6 +69,23 @@ static bool errata_probe_pmu(unsigned int stage,
return true;
}

+static bool errata_probe_write_once(unsigned int stage,
+ unsigned long arch_id, unsigned long impid)
+{
+ if (!IS_ENABLED(CONFIG_ERRATA_THEAD_WRITE_ONCE))
+ return false;
+
+ /* target-c9xx cores report arch_id and impid as 0 */
+ if (arch_id != 0 || impid != 0)
+ return false;
+
+ if (stage == RISCV_ALTERNATIVES_EARLY_BOOT ||
+ stage == RISCV_ALTERNATIVES_MODULE)
+ return true;
+
+ return false;
+}
+
static u32 thead_errata_probe(unsigned int stage,
unsigned long archid, unsigned long impid)
{
@@ -83,6 +100,9 @@ static u32 thead_errata_probe(unsigned int stage,
if (errata_probe_pmu(stage, archid, impid))
cpu_req_errata |= BIT(ERRATA_THEAD_PMU);

+ if (errata_probe_write_once(stage, archid, impid))
+ cpu_req_errata |= BIT(ERRATA_THEAD_WRITE_ONCE);
+
return cpu_req_errata;
}

diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
index 712cab7adffe..fbb2b8d39321 100644
--- a/arch/riscv/include/asm/errata_list.h
+++ b/arch/riscv/include/asm/errata_list.h
@@ -11,19 +11,6 @@
#include <asm/hwcap.h>
#include <asm/vendorid_list.h>

-#ifdef CONFIG_ERRATA_SIFIVE
-#define ERRATA_SIFIVE_CIP_453 0
-#define ERRATA_SIFIVE_CIP_1200 1
-#define ERRATA_SIFIVE_NUMBER 2
-#endif
-
-#ifdef CONFIG_ERRATA_THEAD
-#define ERRATA_THEAD_PBMT 0
-#define ERRATA_THEAD_CMO 1
-#define ERRATA_THEAD_PMU 2
-#define ERRATA_THEAD_NUMBER 3
-#endif
-
#ifdef __ASSEMBLY__

#define ALT_INSN_FAULT(x) \
diff --git a/arch/riscv/include/asm/rwonce.h b/arch/riscv/include/asm/rwonce.h
new file mode 100644
index 000000000000..be0b8864969d
--- /dev/null
+++ b/arch/riscv/include/asm/rwonce.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_RWONCE_H
+#define __ASM_RWONCE_H
+
+#include <linux/compiler_types.h>
+#include <asm/alternative-macros.h>
+#include <asm/vendorid_list.h>
+
+#define __WRITE_ONCE(x, val) \
+do { \
+ *(volatile typeof(x) *)&(x) = (val); \
+ asm volatile(ALTERNATIVE( \
+ __nops(1), \
+ "fence w, o\n\t", \
+ THEAD_VENDOR_ID, \
+ ERRATA_THEAD_WRITE_ONCE, \
+ CONFIG_ERRATA_THEAD_WRITE_ONCE) \
+ : : : "memory"); \
+} while (0)
+
+#include <asm-generic/rwonce.h>
+
+#endif /* __ASM_RWONCE_H */
diff --git a/arch/riscv/include/asm/vendorid_list.h b/arch/riscv/include/asm/vendorid_list.h
index cb89af3f0704..73078cfe4029 100644
--- a/arch/riscv/include/asm/vendorid_list.h
+++ b/arch/riscv/include/asm/vendorid_list.h
@@ -8,4 +8,18 @@
#define SIFIVE_VENDOR_ID 0x489
#define THEAD_VENDOR_ID 0x5b7

+#ifdef CONFIG_ERRATA_SIFIVE
+#define ERRATA_SIFIVE_CIP_453 0
+#define ERRATA_SIFIVE_CIP_1200 1
+#define ERRATA_SIFIVE_NUMBER 2
+#endif
+
+#ifdef CONFIG_ERRATA_THEAD
+#define ERRATA_THEAD_PBMT 0
+#define ERRATA_THEAD_CMO 1
+#define ERRATA_THEAD_PMU 2
+#define ERRATA_THEAD_WRITE_ONCE 3
+#define ERRATA_THEAD_NUMBER 4
+#endif
+
#endif
diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
index 8d0a6280e982..fb07fe8c6e45 100644
--- a/include/asm-generic/rwonce.h
+++ b/include/asm-generic/rwonce.h
@@ -50,10 +50,12 @@
__READ_ONCE(x); \
})

+#ifndef __WRITE_ONCE
#define __WRITE_ONCE(x, val) \
do { \
*(volatile typeof(x) *)&(x) = (val); \
} while (0)
+#endif

#define WRITE_ONCE(x, val) \
do { \