1 files changed, 14 insertions, 0 deletions
diff --git a/library/std/src/time.rs b/library/std/src/time.rs
index e9207ee3617..5e2ce6d3f46 100644
--- a/library/std/src/time.rs
+++ b/library/std/src/time.rs
@@ -263,6 +263,20 @@ impl Instant {
         //
         // To hopefully mitigate the impact of this, a few platforms are
         // excluded as "these at least haven't gone backwards yet".
+        //
+        // While issues have been seen on arm64 platforms the Arm architecture
+        // requires that the counter monotonically increases and that it must
+        // provide a uniform view of system time (e.g. it must not be possible
+        // for a core to recieve a message from another core with a time stamp
+        // and observe time going backwards (ARM DDI 0487G.b D11.1.2). While
+        // there have been a few 64bit SoCs that have bugs which cause time to
+        // not monoticially increase, these have been fixed in the Linux kernel
+        // and we shouldn't penalize all Arm SoCs for those who refuse to
+        // update their kernels:
+        // SUN50I_ERRATUM_UNKNOWN1 - Allwinner A64 / Pine A64 - fixed in 5.1
+        // FSL_ERRATUM_A008585 - Freescale LS2080A/LS1043A - fixed in 4.10
+        // HISILICON_ERRATUM_161010101 - Hisilicon 1610 - fixed in 4.11
+        // ARM64_ERRATUM_858921 - Cortex A73 - fixed in 4.12
         if time::Instant::actually_monotonic() {
             return Instant(os_now);
         }