On Fri, 5 Mar 2021 at 08:32, Shawn Guo <shawn.guo@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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.
>
I suppose we have to rely on DtbLoader for these platforms anyway,
right? That means we should be able to rely on it to publish a RT_PROP
configuration table which tells the kernel which EFI runtime services
are usable and which are not. This way, we could get rid of
efi=novamap as well.
I'd prefer to rely on that than on DMI quirks - we have not used those
at all on arm64/ARM so far, and the DMI tables are parsed relatively
late, so in some cases, DMI quirks may not be reliable.
