Commit 500de3dd authored by Thomas Renninger's avatar Thomas Renninger Committed by Matthew Garrett

acpi ec_sys: Be more cautious about ec write access

- Set Kconfig option default n
- Only allow root to read/write io file (sever bug!)
- Introduce write support module param -> default off
- Properly clean up if any debugfs files cannot be created
Signed-off-by: default avatarThomas Renninger <>
Signed-off-by: default avatarMatthew Garrett <>
parent de4f1046
......@@ -106,14 +106,19 @@ config ACPI_SYSFS_POWER
tristate "EC read/write access through /sys/kernel/debug/ec"
default y
default n
Say N to disable Embedded Controller /sys/kernel/debug interface
Be aware that using this interface can confuse your Embedded
Controller in a way that a normal reboot is not enough. You then
have to power of your system, and remove the laptop battery for
some seconds.
An Embedded Controller typically is available on laptops and reads
sensor values like battery state and temperature.
The kernel access the EC through ACPI parsed code provided by BIOS
The kernel accesses the EC through ACPI parsed code provided by BIOS
tables. This option allows to access the EC directly without ACPI
code being involved.
Thus this option is a debug option that helps to write ACPI drivers
and can be used to identify ACPI code or EC firmware bugs.
......@@ -17,6 +17,11 @@ MODULE_AUTHOR("Thomas Renninger <>");
MODULE_DESCRIPTION("ACPI EC sysfs access driver");
static bool write_support;
module_param(write_support, bool, 0644);
MODULE_PARM_DESC(write_support, "Dangerous, reboot and removal of battery may "
"be needed.");
#define EC_SPACE_SIZE 256
struct sysdev_class acpi_ec_sysdev_class = {
......@@ -102,6 +107,8 @@ int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
struct dentry *dev_dir;
char name[64];
mode_t mode = 0400;
if (ec_device_count == 0) {
acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
if (!acpi_ec_debugfs_dir)
......@@ -111,17 +118,27 @@ int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
sprintf(name, "ec%u", ec_device_count);
dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
if (!dev_dir) {
if (ec_device_count == 0)
/* TBD: Proper cleanup for multiple ECs */
if (ec_device_count != 0)
goto error;
return -ENOMEM;
debugfs_create_x32("gpe", 0444, dev_dir, (u32 *)&first_ec->gpe);
debugfs_create_bool("use_global_lock", 0444, dev_dir,
(u32 *)&first_ec->global_lock);
debugfs_create_file("io", 0666, dev_dir, ec, &acpi_ec_io_ops);
if (!debugfs_create_x32("gpe", 0444, dev_dir, (u32 *)&first_ec->gpe))
goto error;
if (!debugfs_create_bool("use_global_lock", 0444, dev_dir,
(u32 *)&first_ec->global_lock))
goto error;
if (write_support)
mode = 0600;
if (!debugfs_create_file("io", mode, dev_dir, ec, &acpi_ec_io_ops))
goto error;
return 0;
return -ENOMEM;
static int __init acpi_ec_sys_init(void)
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