[PATCH] arm64: efi: add check for broken efi poweroff

[Shawn Guo]

On Fri, Mar 05, 2021 at 08:01:02AM +0100, Ard Biesheuvel wrote:
> On Fri, 5 Mar 2021 at 07:51, Shawn Guo <shawn.guo at linaro.org> wrote:
> >
> > Poweroff via UEFI Runtime Services doesn't always work on every single
> > arm64 machine.  For example, on Lenovo Flex 5G laptop, it results in
> > a system reboot rather than shutdown.  Add a DMI check to keep such
> > system stay with the original poweroff method (PSCI).
> >
> > Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
> 
> What is the point of using EFI runtime services on this machine if
> poweroff doesn't work either?

Hmm, I'm not sure how many EFI runtime services are being used by
kernel, but this is the only one broken I have seen.  Not sure we want
to disable the whole thing completely.  Also, I'm looking at commit log
of 0c5ed61adbdb ("efi/reboot: Allow powering off machines using EFI")
below.

    Not only can EfiResetSystem() be used to reboot, it can also be used to
    power down machines.

    By and large, this functionality doesn't work very well across the range
    of EFI machines in the wild, so it should definitely only be used as a
    last resort. In an ideal world, this wouldn't be needed at all.
    
    Unfortunately, we're starting to see machines where EFI is the *only*
    reliable way to power down, and nothing else, not PCI, not ACPI, works.

It seems poweroff via EFI runtime services is known not working for
every machine, and was meant to be the last resort if nothing else can
power off system.  If we try PSCI first on arm64, you do not see my
patch at all :)

> Can't we just boot this thing with
> efi=noruntime?

We are trying to get arm64 laptop support into distros, and patching
kernel cmdline with 'efi=novamap' is already a pain.  We do not really
want to have more of it.

Shawn