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>

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.