The errata #858921 describes that Cortex-A73 (r0p0 - r0p2)
counter read can return a wrong value when the counter crosses
a 32bit boundary, but newer Cortex-A73 are not affected.
The workaround involves performing the read twice, compare
bit[32] of the two read values. If bit[32] is different,
keep the first value, otherwise keep the second value.
Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
---
arch/arm/arm64/Config.uk | 8 ++++++++
plat/common/arm/time.c | 20 ++++++++++++++++++++
2 files changed, 28 insertions(+)
diff --git a/arch/arm/arm64/Config.uk b/arch/arm/arm64/Config.uk
index 7797516..8c20e68 100644
--- a/arch/arm/arm64/Config.uk
+++ b/arch/arm/arm64/Config.uk
@@ -46,3 +46,11 @@ config MARCH_ARM64_CORTEXA75
Compile for Armv8.2 Cortex-A75 (and compatible) CPUs
endchoice
+
+config ARM64_ERRATUM_858921
+ bool "Workaround for Cortex-A73 erratum 858921"
+ default y
+ help
+ This option enables a workaround for Cortex-A73 (r0p0 - r0p2),
+ whose counter may return a wrong value when the counter crosses
+ a 32-bit boundary. The newer Cortex-A73 are not affected.
diff --git a/plat/common/arm/time.c b/plat/common/arm/time.c
index a84e1a5..93b0521 100644
--- a/plat/common/arm/time.c
+++ b/plat/common/arm/time.c
@@ -63,10 +63,30 @@ static inline uint32_t get_counter_frequency(void)
return SYSREG_READ32(cntfrq_el0);
}
+#ifdef CONFIG_ARM64_ERRATUM_858921
+/*
+ * The errata #858921 describes that Cortex-A73 (r0p0 - r0p2) counter
+ * read can return a wrong value when the counter crosses a 32bit boundary.
+ * But newer Cortex-A73 are not affected.
+ *
+ * The workaround involves performing the read twice, compare bit[32] of
+ * the two read values. If bit[32] is different, keep the first value,
+ * otherwise keep the second value.
+ */
+static uint64_t read_virtual_count(void)
+{
+ uint64_t val_1st, val_2nd;
+
+ val_1st = SYSREG_READ64(cntvct_el0);
+ val_2nd = SYSREG_READ64(cntvct_el0);
+ return (((val_1st ^ val_2nd) >> 32) & 1) ? val_1st : val_2nd;
+}
+#else
static inline uint64_t read_virtual_count(void)
{
return SYSREG_READ64(cntvct_el0);
}
+#endif
/*
* monotonic_clock(): returns # of nanoseconds passed since
