Intel Bay Trail Continues To See Linux Fixes In 2020 - This Time For Time Drifting

It's been seven years since Intel launched the "Bay Trail" Atom processors and the Linux fixes for it and the succeeding Cherry Trail continue to materialize for the kernel.

Over the years we have seen Intel Bay Trail support on Linux seeing quite a number of fixes. The Bay Trail work has included belated items like fixing hibernation support, Bay Trail quirky behavior on varying kernels, improved clocking behavior, performance fixes, and other items. Bay Trail continues to stand out as one of the buggier Intel platforms when it comes to the Linux driver support.

In 2020 the latest we are seeing is a fix for time drifting on select Bay Trail and Cherry Trail devices. The fix isn't coming via Intel but rather Red Hat's Hans de Goede who has taken care of many of the Bay Trail quirks over the years. Now queued in x86/timers is a set of patches by Goede for making the MSR-derived TSC frequency more accurate.

The Red Hat engineer was able to fix the Bay/Cherry Trail issue of time drifting about one second per hour (or about twenty to thirty seconds per day) on some devices that rely upon Linux's TSC_MSR code in determining the TSC frequency. The before/after for the aging Atom hardware:

CPU freq before: CPU freq after:
Intel N2840 2165.800 MHz 2166.667 MHz
Intel Z3736 1332.800 MHz 1333.333 MHz
Intel Z3775 1466.300 MHz 1466.667 MHz

This change should be in place with the forthcoming Linux 5.7 kernel cycle this spring. Longtime overdue, granted, most Intel platforms tend to see great Linux support at (or rather, before) launch but Bay Trail has proven to be the runt of the litter.