efi: Register EFI rtc platform device only when available

Drop the separate driver that registers the EFI rtc on all EFI
systems that have runtime services available, and instead, move
the registration into the core EFI code, and make it conditional
on whether the actual time related services are available.
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/efi.c

@@ -321,6 +321,9 @@ static int __init efisubsys_init(void)
 		}
 	}
 
+	if (efi_rt_services_supported(EFI_RT_SUPPORTED_TIME_SERVICES))
+		platform_device_register_simple("rtc-efi", 0, NULL, 0);
+
 	/* We register the efi directory at /sys/firmware/efi */
 	efi_kobj = kobject_create_and_add("efi", firmware_kobj);
 	if (!efi_kobj) {

drivers/rtc/Makefile

@@ -12,10 +12,6 @@ obj-$(CONFIG_RTC_CLASS)		+= rtc-core.o
 obj-$(CONFIG_RTC_MC146818_LIB)	+= rtc-mc146818-lib.o
 rtc-core-y			:= class.o interface.o
 
-ifdef CONFIG_RTC_DRV_EFI
-rtc-core-y			+= rtc-efi-platform.o
-endif
-
 rtc-core-$(CONFIG_RTC_NVMEM)		+= nvmem.o
 rtc-core-$(CONFIG_RTC_INTF_DEV)		+= dev.o
 rtc-core-$(CONFIG_RTC_INTF_PROC)	+= proc.o

drivers/rtc/rtc-efi-platform.c

-// SPDX-License-Identifier: GPL-2.0
-/*
- * Moved from arch/ia64/kernel/time.c
- *
- * Copyright (C) 1998-2003 Hewlett-Packard Co
- *	Stephane Eranian <eranian@hpl.hp.com>
- *	David Mosberger <davidm@hpl.hp.com>
- * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
- * Copyright (C) 1999-2000 VA Linux Systems
- * Copyright (C) 1999-2000 Walt Drummond <drummond@valinux.com>
- */
-
-#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-
-#include <linux/init.h>
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/efi.h>
-#include <linux/platform_device.h>
-
-static struct platform_device rtc_efi_dev = {
-	.name = "rtc-efi",
-	.id = -1,
-};
-
-static int __init rtc_init(void)
-{
-	if (efi_enabled(EFI_RUNTIME_SERVICES))
-		if (platform_device_register(&rtc_efi_dev) < 0)
-			pr_err("unable to register rtc device...\n");
-
-	/* not necessarily an error */
-	return 0;
-}
-module_init(rtc_init);