Linux supports two methods of overriding the BIOS DSDT:

CONFIG_ACPI_CUSTOM_DSDT builds the image into the kernel.

CONFIG_ACPI_CUSTOM_OVERRIDE_INITRAMFS loads the image from
the initramfs at boot-time. It is more flexible in that it
does not need to be built into the kernel and tables other
than DSDT can potentially be overridden. Please see
Documentation/acpi/table-override.txt for more information.

When to use this method is described in detail on the
Linux/ACPI home page:
http://www.lesswatts.org/projects/acpi/overridingDSDT.php
