2 files changed, 149 insertions, 1 deletions

diff --git a/Documentation/acpi/method-customizing.txt b/Documentation/acpi/method-customizing.txt
new file mode 100644
index 000000000000..e628cd23ca80
--- /dev/null
+++ b/Documentation/acpi/method-customizing.txt
@@ -0,0 +1,66 @@
+Linux ACPI Custom Control Method How To
+=======================================
+
+Written by 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.
+Note: The same ACPI control method can be overridden for many times,
+      and it's always the latest one that used by Linux/kernel.
+
+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)
+      {
+        External (ACON)
+
+        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.
+      And remember to use "External" to declare external objects.
+   e) assemble the file to generate the AML code of the method.
+      e.g. "iasl psr.asl" (psr.aml is generated as a result)
+   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 overrided 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.
diff --git a/drivers/acpi/debug.c b/drivers/acpi/debug.c
index 8a690c3b8e23..cc421b7ae166 100644
--- a/drivers/acpi/debug.c
+++ b/drivers/acpi/debug.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/moduleparam.h>
+#include <linux/debugfs.h>
 #include <asm/uaccess.h>
 #include <acpi/acpi_drivers.h>
 
@@ -196,6 +197,80 @@ module_param_call(trace_state, param_set_trace_state, param_get_trace_state,
                   NULL, 0644);
 
 /* --------------------------------------------------------------------------
+                                DebugFS Interface
+   -------------------------------------------------------------------------- */
+
+static ssize_t cm_write(struct file *file, const char __user *user_buf,
+                        size_t count, loff_t *ppos)
+{
+        static char *buf;
+        static int uncopied_bytes;
+        struct acpi_table_header table;
+        acpi_status status;
+
+        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 = table.length;
+                buf = kzalloc(uncopied_bytes, GFP_KERNEL);
+                if (!buf)
+                        return -ENOMEM;
+        }
+
+        if (uncopied_bytes < count) {
+                kfree(buf);
+                return -EINVAL;
+        }
+
+        if (copy_from_user(buf + (*ppos), user_buf, count)) {
+                kfree(buf);
+                return -EFAULT;
+        }
+
+        uncopied_bytes -= count;
+        *ppos += count;
+
+        if (!uncopied_bytes) {
+                status = acpi_install_method(buf);
+                kfree(buf);
+                if (ACPI_FAILURE(status))
+                        return -EINVAL;
+                add_taint(TAINT_OVERRIDDEN_ACPI_TABLE);
+        }
+
+        return count;
+}
+
+static const struct file_operations cm_fops = {
+        .write = cm_write,
+};
+
+static int acpi_debugfs_init(void)
+{
+        struct dentry *acpi_dir, *cm_dentry;
+
+        acpi_dir = debugfs_create_dir("acpi", NULL);
+        if (!acpi_dir)
+                goto err;
+
+        cm_dentry = debugfs_create_file("custom_method", S_IWUGO,
+                                        acpi_dir, NULL, &cm_fops);
+        if (!cm_dentry)
+                goto err;
+
+        return 0;
+
+err:
+        if (acpi_dir)
+                debugfs_remove(acpi_dir);
+        return -EINVAL;
+}
+
+/* --------------------------------------------------------------------------
                               FS Interface (/proc)
    -------------------------------------------------------------------------- */
 #ifdef CONFIG_ACPI_PROCFS
@@ -286,7 +361,7 @@ static const struct file_operations acpi_system_debug_proc_fops = {
 };
 #endif
 
-int __init acpi_debug_init(void)
+int __init acpi_procfs_init(void)
 {
 #ifdef CONFIG_ACPI_PROCFS
         struct proc_dir_entry *entry;
@@ -321,3 +396,10 @@ int __init acpi_debug_init(void)
         return 0;
 #endif
 }
+
+int __init acpi_debug_init(void)
+{
+        acpi_debugfs_init();
+        acpi_procfs_init();
+        return 0;
+}