ACPI / tables: table override from built-in initrd

In some scenario, we need to build initrd with kernel in a single image.
This can simplify system deployment process by downloading the whole system
once, such as in IC verification.

This patch adds support to override ACPI tables from built-in initrd.
Signed-off-by: Shunyong Yang <shunyong.yang@hxt-semitech.com>
[ rjw: Minor cleanups ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/acpi/initrd_table_override.txt

@@ -14,6 +14,10 @@ upgrade the ACPI execution environment that is defined by the ACPI tables
 via upgrading the ACPI tables provided by the BIOS with an instrumented,
 modified, more recent version one, or installing brand new ACPI tables.
 
+When building initrd with kernel in a single image, option
+ACPI_TABLE_OVERRIDE_VIA_BUILTIN_INITRD should also be true for this
+feature to work.
+
 For a full list of ACPI tables that can be upgraded/installed, take a look
 at the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in
 drivers/acpi/tables.c.

drivers/acpi/Kconfig

@@ -357,6 +357,16 @@ config ACPI_TABLE_UPGRADE
 	  initrd, therefore it's safe to say Y.
 	  See Documentation/acpi/initrd_table_override.txt for details
 
+config ACPI_TABLE_OVERRIDE_VIA_BUILTIN_INITRD
+	bool "Override ACPI tables from built-in initrd"
+	depends on ACPI_TABLE_UPGRADE
+	depends on INITRAMFS_SOURCE!="" && INITRAMFS_COMPRESSION=""
+	help
+	  This option provides functionality to override arbitrary ACPI tables
+	  from built-in uncompressed initrd.
+
+	  See Documentation/acpi/initrd_table_override.txt for details
+
 config ACPI_DEBUG
 	bool "Debug Statements"
 	help

drivers/acpi/tables.c

@@ -473,14 +473,22 @@ static DECLARE_BITMAP(acpi_initrd_installed, NR_ACPI_INITRD_TABLES);
 
 void __init acpi_table_upgrade(void)
 {
-	void *data = (void *)initrd_start;
-	size_t size = initrd_end - initrd_start;
+	void *data;
+	size_t size;
 	int sig, no, table_nr = 0, total_offset = 0;
 	long offset = 0;
 	struct acpi_table_header *table;
 	char cpio_path[32] = "kernel/firmware/acpi/";
 	struct cpio_data file;
 
+	if (IS_ENABLED(CONFIG_ACPI_TABLE_OVERRIDE_VIA_BUILTIN_INITRD)) {
+		data = __initramfs_start;
+		size = __initramfs_size;
+	} else {
+		data = (void *)initrd_start;
+		size = initrd_end - initrd_start;
+	}
+
 	if (data == NULL || size == 0)
 		return;
 

include/linux/initrd.h

@@ -25,3 +25,6 @@ extern phys_addr_t phys_initrd_start;
 extern unsigned long phys_initrd_size;
 
 extern unsigned int real_root_dev;
+
+extern char __initramfs_start[];
+extern unsigned long __initramfs_size;