Re: [PATCH] rtc: efi: restore alarm support with runtime capability probe

[Johnny Fan]

On Fri, Aug 28, 2026 at 09:26:42AM +0200, Ard Biesheuvel wrote:
> Why does it need working alarm/wakeup support?
> 
> I'm not saying we shouldn't bring it back, but this deserves a bit of
> motivation, no?

Hi Ard,

Thanks for the review.

The reason is wakeup: on CIX platforms, the RTC is an I2C device
owned by firmware, and in the ACPI boot configuration the bus is
not exposed to the OS, so the EFI runtime services are the only
way Linux can program the RTC alarm at all. With it removed,
'rtcwake' fails for both suspend-to-RAM and power-off wakeup --
Linux simply has no other path to set an alarm on this platform.

It is also a cross-OS consistency thing: Windows programs the
same alarm through the same runtime services, so a shared
interface that is time-only on the Linux side is asymmetric.

I'll extend the commit message with this motivation in v2.

Thanks,
Johnny