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Subject[PATCH v2 16/18] arm64: arch_timer: Workaround for Cortex-A73 erratum 858921
Date
Cortex-A73 (all versions) counter read can return a wrong value
when the counter crosses a 32bit boundary.

The workaround involves performing the read twice, and to return
one or the other depending on whether a transition has taken place.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
drivers/clocksource/Kconfig | 11 +++++++++++
drivers/clocksource/arm_arch_timer.c | 19 +++++++++++++++++++
2 files changed, 30 insertions(+)

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 3356ab821624..af80a7c44faf 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -366,6 +366,17 @@ config HISILICON_ERRATUM_161010101
161010101. The workaround will be active if the hisilicon,erratum-161010101
property is found in the timer node.

+config ARM64_ERRATUM_858921
+ bool "Workaround for Cortex-A73 erratum 858921"
+ default y
+ select ARM_ARCH_TIMER_OOL_WORKAROUND
+ depends on ARM_ARCH_TIMER && ARM64
+ help
+ This option enables a workaround applicable to Cortex-A73
+ (all versions), whose counter may return incorrect values.
+ The workaround will be dynamically enabled when an affected
+ core is detected.
+
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 eccff0fedf2c..ba4be5859aa4 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -266,6 +266,17 @@ static u64 notrace hisi_161010101_read_cntvct_el0(void)
}
#endif

+#ifdef CONFIG_ARM64_ERRATUM_858921
+static u64 notrace arm64_858921_read_cntvct_el0(void)
+{
+ u64 old, new;
+
+ old = read_sysreg(cntvct_el0);
+ new = read_sysreg(cntvct_el0);
+ return (((old ^ new) >> 32) & 1) ? old : new;
+}
+#endif
+
#ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *,
timer_unstable_counter_workaround);
@@ -331,6 +342,14 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
.set_next_event_virt = erratum_set_next_event_tval_virt,
},
#endif
+#ifdef CONFIG_ARM64_ERRATUM_858921
+ {
+ .match_type = ate_match_local_cap_id,
+ .id = (void *)ARM64_WORKAROUND_858921,
+ .desc = "ARM erratum 858921",
+ .read_cntvct_el0 = arm64_858921_read_cntvct_el0,
+ },
+#endif
};

typedef bool (*ate_match_fn_t)(const struct arch_timer_erratum_workaround *,
--
2.11.0
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