Make some small improvements to the efirtc driver by obtaining the clock
capabilities (resolution and whether the sub-second counters are reset) and
using the info when registering the clock. When the hardware zeroes out the
subsecond info on clock-set, schedule clock updates to happen just before
top-of-second, so that the RTC time is closely in-sync with kernel time.
Also, in the identify() routine, always add the driver if EFI runtime
services are available, then decide in probe() whether to attach the driver
or not. If not attaching and bootverbose is on, say why. All of this is
basically to avoid "silent failure" -- if someone thinks there should be an
efi rtc and it's not attaching, at least they can set bootverbose and maybe
get a clue from the output.
Differential Revision: https://reviews.freebsd.org/D14565 (timed out)
the system time.
As we seem to only read this time on boot, and this is the only source of
time on many arm64 machines we need to enable this by default there. As
this is not always the case with U-Boot firmware, or when we have been
booted from a non-UEFI environment we only enable the device driver when
the Runtime Services are present and reading the time doesn't result in an
error.
PR: 212185
Reviewed by: imp, kib
Tested by: emaste
Relnotes: yes
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D12650
