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

From: Ard Biesheuvel <ardb@kernel.org>
To: Shawn Guo <shawn.guo@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Jeffrey Hugo <jhugo@codeaurora.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH] arm64: efi: add check for broken efi poweroff
Date: Fri, 5 Mar 2021 08:46:35 +0100	[thread overview]
Message-ID: <CAMj1kXEezoDanHsKiN566r0xP1o8pQBk5UZPff0zYxG+Aw7-Og@mail.gmail.com> (raw)
In-Reply-To: <20210305073151.GI17424@dragon>

On Fri, 5 Mar 2021 at 08:32, Shawn Guo <shawn.guo@linaro.org> 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@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@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.
>

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.