+++ /dev/null
-.. SPDX-License-Identifier: GPL-2.0
-
-=======================================
-Linux ACPI Custom Control Method How To
-=======================================
-
-:Author: Zhang Rui <rui.zhang@intel.com>
-
-
-Linux supports customizing ACPI control methods at runtime.
-
-Users can use this to:
-
-1. override an existing method which may not work correctly,
- or just for debugging purposes.
-2. insert a completely new method in order to create a missing
- method such as _OFF, _ON, _STA, _INI, etc.
-
-For these cases, it is far simpler to dynamically install a single
-control method rather than override the entire DSDT, because kernel
-rebuild/reboot is not needed and test result can be got in minutes.
-
-.. note::
-
- - Only ACPI METHOD can be overridden, any other object types like
- "Device", "OperationRegion", are not recognized. Methods
- declared inside scope operators are also not supported.
-
- - The same ACPI control method can be overridden for many times,
- and it's always the latest one that used by Linux/kernel.
-
- - To get the ACPI debug object output (Store (AAAA, Debug)),
- please run::
-
- echo 1 > /sys/module/acpi/parameters/aml_debug_output
-
-
-1. override an existing method
-==============================
-a) get the ACPI table via ACPI sysfs I/F. e.g. to get the DSDT,
- just run "cat /sys/firmware/acpi/tables/DSDT > /tmp/dsdt.dat"
-b) disassemble the table by running "iasl -d dsdt.dat".
-c) rewrite the ASL code of the method and save it in a new file,
-d) package the new file (psr.asl) to an ACPI table format.
- Here is an example of a customized \_SB._AC._PSR method::
-
- DefinitionBlock ("", "SSDT", 1, "", "", 0x20080715)
- {
- Method (\_SB_.AC._PSR, 0, NotSerialized)
- {
- Store ("In AC _PSR", Debug)
- Return (ACON)
- }
- }
-
- Note that the full pathname of the method in ACPI namespace
- should be used.
-e) assemble the file to generate the AML code of the method.
- e.g. "iasl -vw 6084 psr.asl" (psr.aml is generated as a result)
- If parameter "-vw 6084" is not supported by your iASL compiler,
- please try a newer version.
-f) mount debugfs by "mount -t debugfs none /sys/kernel/debug"
-g) override the old method via the debugfs by running
- "cat /tmp/psr.aml > /sys/kernel/debug/acpi/custom_method"
-
-2. insert a new method
-======================
-This is easier than overriding an existing method.
-We just need to create the ASL code of the method we want to
-insert and then follow the step c) ~ g) in section 1.
-
-3. undo your changes
-====================
-The "undo" operation is not supported for a new inserted method
-right now, i.e. we can not remove a method currently.
-For an overridden method, in order to undo your changes, please
-save a copy of the method original ASL code in step c) section 1,
-and redo step c) ~ g) to override the method with the original one.
-
-
-.. note:: We can use a kernel with multiple custom ACPI method running,
- But each individual write to debugfs can implement a SINGLE
- method override. i.e. if we want to insert/override multiple
- ACPI methods, we need to redo step c) ~ g) for multiple times.
-
-.. note:: Be aware that root can mis-use this driver to modify arbitrary
- memory and gain additional rights, if root's privileges got
- restricted (for example if root is not allowed to load additional
- modules after boot).
which is used to report some hardware errors notified via
SCI, mainly the corrected errors.
-config ACPI_CUSTOM_METHOD
- tristate "Allow ACPI methods to be inserted/replaced at run time"
- depends on DEBUG_FS
- help
- This debug facility allows ACPI AML methods to be inserted and/or
- replaced without rebooting the system. For details refer to:
- Documentation/firmware-guide/acpi/method-customizing.rst.
-
- NOTE: This option is security sensitive, because it allows arbitrary
- kernel memory to be written to by root (uid=0) users, allowing them
- to bypass certain security measures (e.g. if root is not allowed to
- load additional kernel modules after boot, this feature may be used
- to override that restriction).
-
config ACPI_BGRT
bool "Boottime Graphics Resource Table support"
depends on EFI && (X86 || ARM64)
+++ /dev/null
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * custom_method.c - debugfs interface for customizing ACPI control method
- */
-
-#include <linux/init.h>
-#include <linux/module.h>
-#include <linux/kernel.h>
-#include <linux/uaccess.h>
-#include <linux/debugfs.h>
-#include <linux/acpi.h>
-#include <linux/security.h>
-
-#include "internal.h"
-
-MODULE_LICENSE("GPL");
-
-static struct dentry *cm_dentry;
-
-/* /sys/kernel/debug/acpi/custom_method */
-
-static ssize_t cm_write(struct file *file, const char __user *user_buf,
- size_t count, loff_t *ppos)
-{
- static char *buf;
- static u32 max_size;
- static u32 uncopied_bytes;
-
- struct acpi_table_header table;
- acpi_status status;
- int ret;
-
- ret = security_locked_down(LOCKDOWN_ACPI_TABLES);
- if (ret)
- return ret;
-
- if (!(*ppos)) {
- /* parse the table header to get the table length */
- if (count <= sizeof(struct acpi_table_header))
- return -EINVAL;
- if (copy_from_user(&table, user_buf,
- sizeof(struct acpi_table_header)))
- return -EFAULT;
- uncopied_bytes = max_size = table.length;
- /* make sure the buf is not allocated */
- kfree(buf);
- buf = kzalloc(max_size, GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
- }
-
- if (buf == NULL)
- return -EINVAL;
-
- if ((*ppos > max_size) ||
- (*ppos + count > max_size) ||
- (*ppos + count < count) ||
- (count > uncopied_bytes)) {
- kfree(buf);
- buf = NULL;
- return -EINVAL;
- }
-
- if (copy_from_user(buf + (*ppos), user_buf, count)) {
- kfree(buf);
- buf = NULL;
- return -EFAULT;
- }
-
- uncopied_bytes -= count;
- *ppos += count;
-
- if (!uncopied_bytes) {
- status = acpi_install_method(buf);
- kfree(buf);
- buf = NULL;
- if (ACPI_FAILURE(status))
- return -EINVAL;
- add_taint(TAINT_OVERRIDDEN_ACPI_TABLE, LOCKDEP_NOW_UNRELIABLE);
- }
-
- return count;
-}
-
-static const struct file_operations cm_fops = {
- .write = cm_write,
- .llseek = default_llseek,
-};
-
-static int __init acpi_custom_method_init(void)
-{
- cm_dentry = debugfs_create_file("custom_method", S_IWUSR,
- acpi_debugfs_dir, NULL, &cm_fops);
- return 0;
-}
-
-static void __exit acpi_custom_method_exit(void)
-{
- debugfs_remove(cm_dentry);
-}
-
-module_init(acpi_custom_method_init);
-module_exit(acpi_custom_method_exit);
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