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: Thomas Renninger <trenn@suse.de>
CC: mjg59@srcf.ucam.org
CC: platform-driver-x86@vger.kernel.org
CC: linux-acpi@vger.kernel.org
CC: astarikovskiy@suse.de
Signed-off-by: Matthew Garrett <mjg@redhat.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index f7226d1bc80..08e0140920e 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -106,14 +106,19 @@ config ACPI_SYSFS_POWER
 
 config ACPI_EC_DEBUGFS
         tristate "EC read/write access through /sys/kernel/debug/ec"
-        default y
+        default n
         help
           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
-          tables.
+          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.