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

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Message-ID: <CAMj1kXG+0hjhNziKMnhKY-uX4V=OBFuS1mUCdZs7VW2DjAsjyg@mail.gmail.com>
Date: Thu, 10 Jul 2025 17:32:30 +1000
From: Ard Biesheuvel <ardb@...nel.org>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: remove the rtc-wakeup capability from default value

On Thu, 10 Jul 2025 at 17:24, Feng Tang <feng.tang@...ux.alibaba.com> wrote:
>
> Add Alexandre Belloni for his view on rtc-efi driver
>
> On Thu, Jul 10, 2025 at 09:33:19AM +1000, Ard Biesheuvel wrote:
> > 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.
>
> Thanks for the explaination! Yes, it's fair to claim the uefi implementation
> on the 2 ARM servers 'broken' :)
>
> I talked with some firmware developers. They said the rtc-alarm service could
> be implemented, while the difficult part is how to notify OS. I submitted a
> request for a correct RT_PROP table.
>
> Meanwhile, given there are quite some platforms (All ARM server I can access)
> don't have the table and not support rtc wakeup service, I'm thinking of adding
> some runtime check for the service in rtc-efi driver, something like:
>
> ---
> diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
> index fa8bf82df948..7ae948aebd11 100644
> --- a/drivers/rtc/rtc-efi.c
> +++ b/drivers/rtc/rtc-efi.c
> @@ -259,6 +259,7 @@ static int __init efi_rtc_probe(struct platform_device *dev)
>         struct rtc_device *rtc;
>         efi_time_t eft;
>         efi_time_cap_t cap;
> +       efi_bool_t enabled, pending;
>
>         /* First check if the RTC is usable */
>         if (efi.get_time(&eft, &cap) != EFI_SUCCESS)
> @@ -272,7 +273,8 @@ static int __init efi_rtc_probe(struct platform_device *dev)
>
>         rtc->ops = &efi_rtc_ops;
>         clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
> -       if (efi_rt_services_supported(EFI_RT_SUPPORTED_WAKEUP_SERVICES))
> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_WAKEUP_SERVICES) &&
> +               efi.get_wakeup_time(&enabled, &pending, &eft) == EFI_SUCCESS)
>                 set_bit(RTC_FEATURE_ALARM_WAKEUP_ONLY, rtc->features);
>         else
>                 clear_bit(RTC_FEATURE_ALARM, rtc->features);
>
> This works on one ARM server I can test kernel with. Any suggestions?
>

I think this is fine - please send it as a proper patch with commit log etc.