>

> How would you handle such a case? I guess a machine which can't provide
> this runtime service would need some more work in its EFI firmware
> before being ready for GRUB, so perhaps this is a moot point.
> 

If no timing is available, you'd need at least return a count of calls
to the get_time function.

> I propose to re-use the existing function grub_datetime2unixtime()
> (which handles correctly the number of days of each month, as well as
> leap years), instead of doing the calculations here. And take into
> account the time_zone member of grub_efi_time_t as well.

get_time is wrong function for getting tsc. You should create a timer
event with 10000 units (=1 ms) and in its callback increase millisecond
counter.

> Also, there is nothing ARM-specific in this function, so I would put it
> in a generic EFI file like kern/efi/efi.c.
> 

it is ARM-specific by exclusion. All other EFI ports have TSC and don't
need to use EFI functions to retrieve it (other than for calibration on
ia64)