arm64: arch_timer: Workaround for Cortex-A73 erratum 858921

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.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 3356ab821624c9f41f1e84560e96b47b2b6695c2..af80a7c44fafd2c57cee13d242e31d22e5db14f2 100644 (file)
--- 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 f8adea258cf09a52a54b6584f735a578f430c52c..8459d19a84f5ac1dc1319105e6bd2bb199be2c8e 100644 (file)
--- 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 *,