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

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Message-ID: <aG9qmV-wzFr7I-Tb@U-2FWC9VHC-2323.local>
Date: Thu, 10 Jul 2025 15:24:09 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Ard Biesheuvel <ardb@...nel.org>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: remove the rtc-wakeup capability from default value

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?

Thanks,
Feng