linux-kernel - Re: [PATCH] efi: remove the rtc-wakeup capability from default value

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Message-ID: <CAMj1kXEkzXsjm0dPhzxB+KdtzqADd4NmafKmw2rKw7mAPBrgdA@mail.gmail.com>
Date: Thu, 10 Jul 2025 09:33:19 +1000
From: Ard Biesheuvel <ardb@...nel.org>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: remove the rtc-wakeup capability from default value

On Wed, 9 Jul 2025 at 21:00, Feng Tang <feng.tang@...ux.alibaba.com> wrote:
>
> On Wed, Jul 09, 2025 at 08:42:24PM +1000, Ard Biesheuvel wrote:
> > On Wed, 9 Jul 2025 at 20:35, Feng Tang <feng.tang@...ux.alibaba.com> wrote:
> > >
> > > The kernel selftest of rtc reported a error on an ARM server:
> > >
> > >         RUN           rtc.alarm_alm_set ...
> > >         rtctest.c:262:alarm_alm_set:Alarm time now set to 17:31:36.
> > >         rtctest.c:267:alarm_alm_set:Expected -1 (-1) != rc (-1)
> > >         alarm_alm_set: Test terminated by assertion
> > >                  FAIL  rtc.alarm_alm_set
> > >         not ok 5 rtc.alarm_alm_set
> > >
> > > The root cause is, the unerlying EFI firmware doesn't support wakeup
> > > service (get/set alarm), while it doesn't have the efi 'RT_PROP'
> > > table either. The current code logic will claim efi supports these
> > > runtime service capability by default, and let following 'RT_PROP'
> > > table parsing to correct it, if that table exists.
> > >
> > > This issue was reproduced on ARM server from another verndor, and not
> > > reproudce on one x86 server (Icelake). All these 3 platforms don't have
> > > 'RT_PROP' tables, so they are all claimed to support alarm service,
> > > but x86 server uses real CMOS RTC device instead rtc-efi device, and
> > > passes the test.
> > >
> > > So remove the wakeup/alarm capability from default value, and setup
> > > the capability bits according to the 'RT_PROP' table parsing.
> > >
> >
> > What does this achieve? The test result is accurate, as the platform
> > violates the spec by not implementing the RTC wakeup services, and not
> > setting the RT_PROP table bits accordingly.
> >
> > What do we gain by pretending that the platform is not broken, and
> > lying about it?
>
> I don't have much experience with EFI, so I might be totally wrong. I
> don't think not providing the RT_PROP table is 'broken', that's why I
> tried to borrow platforms from different vendors to do the check, which
> all have no this table.
>
> For platform which have no 'RT_PROP' tables (seems to be not a rare case),
> claiming them support all efi runtime service may be kind of risky.
>

It is the other way around. The UEFI spec mandates that all runtime
services are implemented, unless a RT_PROP table is provided.