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Message-Id: <20241214143039.4139398-3-guoren@kernel.org>
Date: Sat, 14 Dec 2024 09:30:39 -0500
From: guoren@...nel.org
To: guoren@...nel.org,
conor@...nel.org,
alexghiti@...osinc.com
Cc: linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org,
paul.walmsley@...ive.com,
palmer@...belt.com,
bjorn@...osinc.com,
leobras@...hat.com,
corbet@....net,
peterlin@...estech.com,
Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH 2/2] riscv: qspinlock: errata: Add ERRATA_THEAD_WRITE_ONCE fixup
From: Guo Ren <guoren@...ux.alibaba.com>
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().
This problem is only observed on the sg2042 hardware platform by
running the lock_torture test program for half an hour. The problem
was not found in the user space application, because interrupt can
break the livelock.
Reviewed-by: Leonardo Bras <leobras@...hat.com>
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
---
arch/riscv/Kconfig.errata | 19 +++++++++++++++
arch/riscv/errata/thead/errata.c | 20 ++++++++++++++++
arch/riscv/include/asm/rwonce.h | 33 ++++++++++++++++++++++++++
arch/riscv/include/asm/vendorid_list.h | 3 ++-
include/asm-generic/rwonce.h | 2 ++
5 files changed, 76 insertions(+), 1 deletion(-)
create mode 100644 arch/riscv/include/asm/rwonce.h
diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
index 2acc7d876e1f..fd6ba85b7a72 100644
--- a/arch/riscv/Kconfig.errata
+++ b/arch/riscv/Kconfig.errata
@@ -119,4 +119,23 @@ 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 of sg2042 & th1520 have 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 signifi-
+ cant 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 beh-
+ avior 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 e24770a77932..dd41f0221fe9 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -142,6 +142,23 @@ 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_BOOT ||
+ stage == RISCV_ALTERNATIVES_MODULE)
+ return true;
+
+ return false;
+}
+
static u32 thead_errata_probe(unsigned int stage,
unsigned long archid, unsigned long impid)
{
@@ -155,6 +172,9 @@ 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/rwonce.h b/arch/riscv/include/asm/rwonce.h
new file mode 100644
index 000000000000..756586746a4f
--- /dev/null
+++ b/arch/riscv/include/asm/rwonce.h
@@ -0,0 +1,33 @@
+/* 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>
+
+#if defined(CONFIG_ERRATA_THEAD_WRITE_ONCE) && !defined(NO_ALTERNATIVE)
+
+#define write_once_fence() \
+do { \
+ asm volatile(ALTERNATIVE( \
+ "nop", \
+ "fence w, o", \
+ THEAD_VENDOR_ID, \
+ ERRATA_THEAD_WRITE_ONCE, \
+ CONFIG_ERRATA_THEAD_WRITE_ONCE) \
+ : : : "memory"); \
+} while (0)
+
+#define __WRITE_ONCE(x, val) \
+do { \
+ *(volatile typeof(x) *)&(x) = (val); \
+ write_once_fence(); \
+} while (0)
+
+#endif /* defined(CONFIG_ERRATA_THEAD_WRITE_ONCE) && !defined(NO_ALTERNATIVE) */
+
+#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 7a387368633a..d5a6e3963feb 100644
--- a/arch/riscv/include/asm/vendorid_list.h
+++ b/arch/riscv/include/asm/vendorid_list.h
@@ -23,7 +23,8 @@
#ifdef CONFIG_ERRATA_THEAD
#define ERRATA_THEAD_MAE 0
#define ERRATA_THEAD_PMU 1
-#define ERRATA_THEAD_NUMBER 2
+#define ERRATA_THEAD_WRITE_ONCE 2
+#define ERRATA_THEAD_NUMBER 3
#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 { \
--
2.40.1
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