System time doesn't sync with RTC time on boot

[Jesse Sung]

== Impact ==
Although we have CONFIG_RTC_HCTOSYS enabled and set CONFIG_RTC_HCTOSYS_DEVICE to "rtc0", system time would only be set if the RTC driver is built-in. This may not be an issue on most amd64 systems because CONFIG_RTC_DRV_CMOS is y for amd64, however it is an issue for other architectures since there may not be a proper RTC driver enabled as built-in. Also making every RTC driver that may be used as built-in is not a good option.

== Fix ==
The commit is in mainline since v5.7:

commit f9b2a4d6a5f18e0aaf715206a056565c56889d9f
Author: Steve Muckle <email address hidden>
Date: Wed Nov 6 11:46:25 2019 -0800

    rtc: class: support hctosys from modular RTC drivers

    Due to distribution constraints it may not be possible to statically
    compile the required RTC driver into the kernel.

    Expand RTC_HCTOSYS support to cover all RTC devices (statically compiled
    or not) by checking at the end of RTC device registration whether the
    time should be synced.

    Signed-off-by: Steve Muckle <email address hidden>
    Link: https://<email address hidden>
    Signed-off-by: Alexandre Belloni <email address hidden>

== Risk of Regression ==
It's a clean cherry-pick for v5.4 and looks straight forward so risk should be low.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1952077

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Jesse Sung (wenchien)]

The patch was NAKed: https://lists.ubuntu.com/archives/kernel-team/2021-November/126087.html

Change the status back to confirmed.