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>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index ccf6ea95f68c..0442ae153a24 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -274,6 +274,23 @@ config ACPI_CUSTOM_DSDT_FILE
           Enter the full path name to the file which includes the AmlCode
           declaration.
 
+config ACPI_CUSTOM_DSDT_INITRD
+        bool "Read Custom DSDT from initramfs"
+        depends on BLK_DEV_INITRD
+        default n
+        help
+          The DSDT (Differentiated System Description Table) often needs to be
+          overridden because of broken BIOS implementations. If this feature is
+          activated you will be able to provide a customized DSDT by adding it
+          to your initramfs. If your mkinitrd tool does not support this feature
+          a script is provided in the documentation. For more details see
+          <file:Documentation/dsdt-initrd.txt> or <http://gaugusch.at/kernel.shtml>.
+          If there is no table found, it will fall-back to the custom DSDT
+          in-kernel (if activated) or to the DSDT from the BIOS.
+
+          Even if you do not need a new one at the moment, you may want to use a
+          better DSDT later. It is safe to say Y here.
+
 config ACPI_BLACKLIST_YEAR
         int "Disable ACPI for systems before Jan 1st this year" if X86_32
         default 0