[PATCH] x86/efi: autoload efivars

["Lee, Chun-Yi" <joeyli.kernel-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

The original patch is from Ben Hutchings's contribution to debian
kernel. Got Ben's permission to remove the code of efi-pstore.c and
then patch to linux-efi:
https://github.com/BlankOn/linux-debian/blob/master/debian/patches/features/all/efi-autoload-efivars.patch

efivars is generally useful to have on EFI systems, and in some cases
it may be impossible to load it after a kernel upgrade in order to
complete a boot loader update. At the same time we don't want to waste
memory on non-EFI systems by making them built-in.

Instead, give them module aliases as if they are platform drivers, and
register a corresponding platform device whenever EFI runtime services
are available.  This should trigger udev to load them.

Cc: Ben Hutchings <ben-/+tVBieCtBitmTQ+vhA3Yw@public.gmane.org>
Cc: Matt Fleming <matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Signed-off-by: Lee, Chun-Yi <jlee-IBi9RG/b67k@public.gmane.org>
---
 arch/x86/platform/efi/efi.c    | 15 +++++++++++++++
 drivers/firmware/efi/efivars.c |  1 +
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 87fc96b..c295c08 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -44,6 +44,7 @@
 #include <linux/io.h>
 #include <linux/reboot.h>
 #include <linux/bcd.h>
+#include <linux/platform_device.h>
 
 #include <asm/setup.h>
 #include <asm/efi.h>
@@ -780,6 +781,20 @@ void __init efi_late_init(void)
 	efi_bgrt_init();
 }
 
+#ifdef CONFIG_EFI_VARS_MODULE
+static int __init efi_load_efivars(void)
+{
+	struct platform_device *pdev;
+
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return 0;
+
+	pdev = platform_device_register_simple("efivars", 0, NULL, 0);
+	return IS_ERR(pdev) ? PTR_ERR(pdev) : 0;
+}
+device_initcall(efi_load_efivars);
+#endif
+
 void __init efi_set_executable(efi_memory_desc_t *md, bool executable)
 {
 	u64 addr, npages;
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 463c565..f256ecd 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -78,6 +78,7 @@ MODULE_AUTHOR("Matt Domsch <Matt_Domsch-DYMqY+WieiM@public.gmane.org>");
 MODULE_DESCRIPTION("sysfs interface to EFI Variables");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(EFIVARS_VERSION);
+MODULE_ALIAS("platform:efivars");
 
 LIST_HEAD(efivar_sysfs_list);
 EXPORT_SYMBOL_GPL(efivar_sysfs_list);
-- 
1.8.4.5