ACPI: basic initramfs DSDT override support

The basics of DSDT from initramfs. In case this option is selected,
populate_rootfs() is called a bit earlier to have the initramfs content
available during ACPI initialization.

This is a very similar path to the one available at
http://gaugusch.at/kernel.shtml but with some update in the
documentation, default set to No and the change of populate_rootfs() the
"Jeff Mahony way" (which avoids reading the initramfs twice).

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Eric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Len Brown <len.brown@intel.com>

2 files changed, 14 insertions, 1 deletions

diff --git a/init/initramfs.c b/init/initramfs.c
index d53fee8d8604..c0b1e0533d80 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -538,7 +538,7 @@ skip:
         initrd_end = 0;
 }
 
-static int __init populate_rootfs(void)
+int __init populate_rootfs(void)
 {
         char *err = unpack_to_rootfs(__initramfs_start,
                          __initramfs_end - __initramfs_start, 0);
@@ -577,4 +577,10 @@ static int __init populate_rootfs(void)
         }
         return 0;
 }
+#ifndef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+/*
+ * if this option is enabled, populate_rootfs() is called _earlier_ in the
+ * boot sequence. This insures that the ACPI initialisation can find the file.
+ */
 rootfs_initcall(populate_rootfs);
+#endif
diff --git a/init/main.c b/init/main.c
index c691f5f7fc27..2a78932f6c07 100644
--- a/init/main.c
+++ b/init/main.c
@@ -102,6 +102,12 @@ static inline void mark_rodata_ro(void) { }
 extern void tc_init(void);
 #endif
 
+#ifdef CONFIG_ACPI_CUSTOM_DSDT_INITRD
+extern int populate_rootfs(void);
+#else
+static inline void populate_rootfs(void) {}
+#endif
+
 enum system_states system_state;
 EXPORT_SYMBOL(system_state);
 
@@ -648,6 +654,7 @@ asmlinkage void __init start_kernel(void)
 
         check_bugs();
 
+        populate_rootfs(); /* For DSDT override from initramfs */
         acpi_early_init(); /* before LAPIC and SMP init */
 
         /* Do the rest non-__init'ed, we're now alive */