[PATCH] rtc: efi: Add runtime check for the wakeup service capability

[Feng Tang <feng.tang@linux.alibaba.com>]

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@linux.alibaba.com>
---
 drivers/rtc/rtc-efi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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)