[PATCH v5 3/6] arm64: arch_timer: Work around Erratum Hisilicon-161601

Erratum Hisilicon-161601 says that the ARM generic timer counter "has the
potential to contain an erroneous value when the timer value changes".
Accesses to TVAL (both read and write) are also affected due to the implicit counter
read.  Accesses to CVAL are not affected.

The workaround is to reread the system count registers until the value of the second
read is larger than the first one by less than 32, the system counter can be guaranteed
not to return wrong value twice by back-to-back read and the error value is always larger
than the correct one by 32. Writes to TVAL are replaced with an equivalent write to CVAL.

The workaround is enabled if the hisilicon,erratum-161601 property is found in
the timer node in the device tree. This can be overridden with the
clocksource.arm_arch_timer.hisilicon-161601 boot parameter, which allows KVM
users to enable the workaround until a mechanism is implemented to
automatically communicate this information.

Fix some description for fsl erratum a008585.

v2: Significant rework based on feedback, including seperate the fsl erratum a008585
    to another patch, update the erratum name and remove unwanted code.

v3: Significant rework based on feedback, including fix some alignment problem, make the
    #define __hisi_161601_read_reg to be private to the .c file instead of being globally
    visible, add more accurate annotation and modify a bit of logical format to enable
    arch_timer_read_ool_enabled, remove the kernel commandline parameter
    clocksource.arm_arch_timer.hisilicon-161601.

v5: Theoretically the erratum should not occur more than twice in succession when reading
    the system counter, but it is possible that some interrupts may lead to more than twice
    read errors, triggering the warning, so setting the number of retries to 50 which is far
    beyond the number of iterations the loop has been observed to take.

Signed-off-by: Ding Tianhong <redacted>
---
 Documentation/arm64/silicon-errata.txt |  1 +
 arch/arm64/include/asm/arch_timer.h    |  2 +-
 drivers/clocksource/Kconfig            |  9 +++++
 drivers/clocksource/arm_arch_timer.c   | 70 +++++++++++++++++++++++++++++++---
 4 files changed, 76 insertions(+), 6 deletions(-)

diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
index 405da11..1c1a95f 100644
--- a/Documentation/arm64/silicon-errata.txt
+++ b/Documentation/arm64/silicon-errata.txt

@@ -63,3 +63,4 @@ stable kernels.
 | Cavium         | ThunderX SMMUv2 | #27704          | N/A		       |
 |                |                 |                 |                         |
 | Freescale/NXP  | LS2080A/LS1043A | A-008585        | FSL_ERRATUM_A008585     |
+| Hisilicon      | Hip0{5,6,7}     | #161601         | HISILICON_ERRATUM_161601|

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index f882c7c..ebf4cde 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h

@@ -29,7 +29,7 @@
 
 #include <clocksource/arm_arch_timer.h>
 
-#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585)
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 extern struct static_key_false arch_timer_read_ool_enabled;
 #define needs_unstable_timer_counter_workaround() \
 	static_branch_unlikely(&arch_timer_read_ool_enabled)

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 4866f7a..162d820 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig

@@ -335,6 +335,15 @@ config FSL_ERRATUM_A008585
 	  value").  The workaround will only be active if the
 	  fsl,erratum-a008585 property is found in the timer node.
 
+config HISILICON_ERRATUM_161601
+	bool "Workaround for Hisilicon Erratum 161601"
+	default y
+	depends on ARM_ARCH_TIMER && ARM64
+	help
+	  This option enables a workaround for Hisilicon Erratum
+	  161601. The workaround will be active if the hisilicon,erratum-161601
+	  property is found in the timer node.
+
 config ARM_GLOBAL_TIMER
 	bool "Support for the ARM global timer" if COMPILE_TEST
 	select CLKSRC_OF if OF

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index e7406ad..9a82496 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c

@@ -95,15 +95,18 @@ static int __init early_evtstrm_cfg(char *buf)
  * Architected system timer support.
  */
 
-#ifdef CONFIG_FSL_ERRATUM_A008585
+#if CONFIG_FSL_ERRATUM_A008585 || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 struct arch_timer_erratum_workaround *timer_unstable_counter_workaround = NULL;
 EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
 

+
+static struct arch_timer_erratum_workaround arch_timer_hisi_161601 = {
+	.erratum = HISILICON_161601,

+	.read_cntp_tval_el0 = hisi_161601_read_cntp_tval_el0,
+	.read_cntv_tval_el0 = hisi_161601_read_cntv_tval_el0,
+	.read_cntvct_el0 = hisi_161601_read_cntvct_el0,
+};
+#endif /* CONFIG_HISILICON_ERRATUM_161601 */

-#ifdef CONFIG_FSL_ERRATUM_A008585
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 		/*
 		 * Don't use the vdso fastpath if errata require using
 		 * the out-of-line counter accessor.

@@ -909,10 +960,19 @@ static int __init arch_timer_of_init(struct device_node *np)
 #ifdef CONFIG_FSL_ERRATUM_A008585
 	if (!timer_unstable_counter_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
 		timer_unstable_counter_workaround = &arch_timer_fsl_a008585;
+#endif
+
+#ifdef CONFIG_HISILICON_ERRATUM_161601
+	if (!timer_unstable_counter_workaround && of_property_read_bool(np, "hisilicon,erratum-161601"))
+		timer_unstable_counter_workaround = &arch_timer_hisi_161601;
+#endif
 
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 	if (timer_unstable_counter_workaround) {
 		static_branch_enable(&arch_timer_read_ool_enabled);
-		pr_info("Enabling workaround for FSL erratum A-008585\n");
+		pr_info("Enabling workaround for %s\n",
+			timer_unstable_counter_workaround->erratum == FSL_A008585 ?
+			"FSL ERRATUM A-008585" : "HISILICON ERRATUM 161601");