[PATCH v2] ACPI / tables: table override from built-in initrd

[Shunyong Yang <shunyong.yang@hxt-semitech.com>]

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.

Cc: Joey Zheng <yu.zheng@hxt-semitech.com>
Signed-off-by: Shunyong Yang <shunyong.yang@hxt-semitech.com>
---
v2: change "upgrade" to "override" as it's more accurate
---
 Documentation/acpi/initrd_table_override.txt |  4 ++++
 drivers/acpi/Kconfig                         | 10 ++++++++++
 drivers/acpi/tables.c                        | 12 ++++++++++--
 include/linux/initrd.h                       |  3 +++
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt
index eb651a6aa285..324d5fb90a22 100644
--- a/Documentation/acpi/initrd_table_override.txt
+++ b/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
+purpose.
+
 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.
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 7cea769c37df..3b362a1c7685 100644
--- a/drivers/acpi/Kconfig
+++ b/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=""
+	def_bool n
+	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
diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 61203eebf3a1..f6a2c5ebabcd 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -473,14 +473,22 @@ static u8 __init acpi_table_checksum(u8 *buffer, u32 length)
 
 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;
 
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
index 84b423044088..02d94aae54c7 100644
--- a/include/linux/initrd.h
+++ b/include/linux/initrd.h
@@ -22,3 +22,6 @@
 extern void free_initrd_mem(unsigned long, unsigned long);
 
 extern unsigned int real_root_dev;
+
+extern char __initramfs_start[];
+extern unsigned long __initramfs_size;
-- 
1.8.3.1