[PATCH 2/2] efi: don't register rtc-efi if the ACPI TAD can drive the RTC

[Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>]

EFI runtime services are best avoided where possible, and ACPI defines a
standard interface to the real time clock in the form of the Time and
Alarm Device (TAD), which the acpi-tad driver has been exposing as an
RTC class device since commit 8a1e7f4b1764 ("ACPI: TAD: Add RTC class
device interface").

So, don't register the rtc-efi platform device if acpi-tad is going to
register an RTC class device for the TAD, according to
acpi_tad_rtc_available().

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
---
 drivers/firmware/efi/efi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 9bc22de0d..706064479 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -34,6 +34,8 @@
 #include <linux/security.h>
 #include <linux/notifier.h>
 
+#include <acpi/acpi_tad.h>
+
 #include <asm/early_ioremap.h>
 
 struct efi __read_mostly efi = {
@@ -459,7 +461,8 @@ static int __init efisubsys_init(void)
 	if (!efi_enabled(EFI_BOOT))
 		return 0;
 
-	if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES))
+	if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES) &&
+	    !acpi_tad_rtc_available())
 		platform_device_register_simple("rtc-efi", 0, NULL, 0);
 
 	/* We register the efi directory at /sys/firmware/efi */
-- 
2.56.0