linux-kernel - Re: [PATCH] rtc: efi: Add runtime check for the wakeup service capability

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Message-ID: <CAMj1kXGiixvwsSmOz65F=OXQuHovO4DMAsJaPZ2sL3PBbMHh8A@mail.gmail.com>
Date: Fri, 11 Jul 2025 11:26:18 +1000
From: Ard Biesheuvel <ardb@...nel.org>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>, linux-rtc@...r.kernel.org, 
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: efi: Add runtime check for the wakeup service capability

On Fri, 11 Jul 2025 at 11:06, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Thu, 10 Jul 2025 at 18:41, Feng Tang <feng.tang@...ux.alibaba.com> wrote:
> >
> > The kernel selftest of rtc reported a error on an ARM server which
> > use rtc-efi device:
> >
> >         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 underlying EFI firmware doesn't support wakeup
> > service (get/set alarm), while it doesn't have the EFI RT_PROP table
> > either. As Ard Biesheuvel clarified [1], this breaks the UEFI spec,
> > which requires EFI firmware to provide a 'RT_PROP' table if it doesn't
> > support all runtime services (Section 4.6.2, UEFI spec 2.10).
> >
> > This issue was also reproduced on ARM server from another vendor, which
> > doesn't have RT_PROP table either. This means, in real world, there are
> > quite some platforms having this issue, that it doesn't support wakeup
> > service while not providing a correct RT_PROP table, which makes it
> > wrongly claimed to support it.
> >
> > Add a runtime check for the wakeup service to detect and correct this
> > kind of cases.
> >
> > [1]. https://lore.kernel.org/lkml/CAMj1kXEkzXsjm0dPhzxB+KdtzqADd4NmafKmw2rKw7mAPBrgdA@mail.gmail.com/
> >
> > Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>
> > ---
> >  drivers/rtc/rtc-efi.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
>
> Thanks, I've queued this up now.
>

Actually, we might just remove the EFI get/set wakeup time
functionality altogether, as it seems rather pointless to me to begin
with.

I'll send out an RFC shortly.