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

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Message-ID: <CAMj1kXHDFq3FZj4134CTcQZnke4t1=u6iRNNsQBvuhb3F6KurQ@mail.gmail.com>
Date: Fri, 11 Jul 2025 11:06:13 +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 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.

> diff --git a/drivers/rtc/rtc-efi.c b/drivers/rtc/rtc-efi.c
> index fa8bf82df948..8d1b9bde6f66 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);
> --
> 2.39.5 (Apple Git-154)
>
>