3 files changed, 67 insertions, 0 deletions

diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
index 1f09d043d086..ddb8ce5333ba 100644
--- a/Documentation/arm64/silicon-errata.txt
+++ b/Documentation/arm64/silicon-errata.txt
@@ -44,6 +44,8 @@ stable kernels.
 
 | Implementor    | Component       | Erratum ID      | Kconfig                     |
 +----------------+-----------------+-----------------+-----------------------------+
+| Allwinner      | A64/R18         | UNKNOWN1        | SUN50I_ERRATUM_UNKNOWN1     |
+|                |                 |                 |                             |
 | ARM            | Cortex-A53      | #826319         | ARM64_ERRATUM_826319        |
 | ARM            | Cortex-A53      | #827319         | ARM64_ERRATUM_827319        |
 | ARM            | Cortex-A53      | #824069         | ARM64_ERRATUM_824069        |
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index a9e26f6a81a1..8dfd3bc448d0 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -360,6 +360,16 @@ config ARM64_ERRATUM_858921
           The workaround will be dynamically enabled when an affected
           core is detected.
 
+config SUN50I_ERRATUM_UNKNOWN1
+        bool "Workaround for Allwinner A64 erratum UNKNOWN1"
+        default y
+        depends on ARM_ARCH_TIMER && ARM64 && ARCH_SUNXI
+        select ARM_ARCH_TIMER_OOL_WORKAROUND
+        help
+          This option enables a workaround for instability in the timer on
+          the Allwinner A64 SoC. The workaround will only be active if the
+          allwinner,erratum-unknown1 property is found in the timer node.
+
 config ARM_GLOBAL_TIMER
         bool "Support for the ARM global timer" if COMPILE_TEST
         select TIMER_OF if OF
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9a7d4dc00b6e..a8b20b65bd4b 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -326,6 +326,48 @@ static u64 notrace arm64_1188873_read_cntvct_el0(void)
 }
 #endif
 
+#ifdef CONFIG_SUN50I_ERRATUM_UNKNOWN1
+/*
+ * The low bits of the counter registers are indeterminate while bit 10 or
+ * greater is rolling over. Since the counter value can jump both backward
+ * (7ff -> 000 -> 800) and forward (7ff -> fff -> 800), ignore register values
+ * with all ones or all zeros in the low bits. Bound the loop by the maximum
+ * number of CPU cycles in 3 consecutive 24 MHz counter periods.
+ */
+#define __sun50i_a64_read_reg(reg) ({                                   \
+        u64 _val;                                                       \
+        int _retries = 150;                                             \
+                                                                        \
+        do {                                                            \
+                _val = read_sysreg(reg);                                \
+                _retries--;                                             \
+        } while (((_val + 1) & GENMASK(9, 0)) <= 1 && _retries);        \
+                                                                        \
+        WARN_ON_ONCE(!_retries);                                        \
+        _val;                                                           \
+})
+
+static u64 notrace sun50i_a64_read_cntpct_el0(void)
+{
+        return __sun50i_a64_read_reg(cntpct_el0);
+}
+
+static u64 notrace sun50i_a64_read_cntvct_el0(void)
+{
+        return __sun50i_a64_read_reg(cntvct_el0);
+}
+
+static u32 notrace sun50i_a64_read_cntp_tval_el0(void)
+{
+        return read_sysreg(cntp_cval_el0) - sun50i_a64_read_cntpct_el0();
+}
+
+static u32 notrace sun50i_a64_read_cntv_tval_el0(void)
+{
+        return read_sysreg(cntv_cval_el0) - sun50i_a64_read_cntvct_el0();
+}
+#endif
+
 #ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
 DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround);
 EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
@@ -423,6 +465,19 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
                 .read_cntvct_el0 = arm64_1188873_read_cntvct_el0,
         },
 #endif
+#ifdef CONFIG_SUN50I_ERRATUM_UNKNOWN1
+        {
+                .match_type = ate_match_dt,
+                .id = "allwinner,erratum-unknown1",
+                .desc = "Allwinner erratum UNKNOWN1",
+                .read_cntp_tval_el0 = sun50i_a64_read_cntp_tval_el0,
+                .read_cntv_tval_el0 = sun50i_a64_read_cntv_tval_el0,
+                .read_cntpct_el0 = sun50i_a64_read_cntpct_el0,
+                .read_cntvct_el0 = sun50i_a64_read_cntvct_el0,
+                .set_next_event_phys = erratum_set_next_event_tval_phys,
+                .set_next_event_virt = erratum_set_next_event_tval_virt,
+        },
+#endif
 };
 
 typedef bool (*ate_match_fn_t)(const struct arch_timer_erratum_workaround *,