thinkpad-acpi: restrict access to some firmware LEDs

Some of the ThinkPad LEDs indicate critical conditions that can cause
data loss or cause hardware damage when ignored (e.g. force-ejecting
a powered up bay; ignoring a failing battery, or empty battery; force-
undocking with the dock buses still active, etc).

On almost all ThinkPads, LED access is write-only, and the firmware
usually does fire-and-forget signaling on them, so you effectively
lose whatever message the firmware was trying to convey to the user
when you override the LED state, without any chance to restore it.

Restrict access to all LEDs that can convey important alarms, or that
could mislead the user into incorrectly operating the hardware.  This
will make the Lenovo engineers less unhappy about the whole issue.

Allow users that really want it to still control all LEDs, it is the
unaware user that we have to worry about.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index 3608081bc3e0..d45c6ab729f8 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -226,6 +226,30 @@ config THINKPAD_ACPI_DEBUG
 
           If you are not sure, say N here.
 
+config THINKPAD_ACPI_UNSAFE_LEDS
+        bool "Allow control of important LEDs (unsafe)"
+        depends on THINKPAD_ACPI
+        default n
+        ---help---
+          Overriding LED state on ThinkPads can mask important
+          firmware alerts (like critical battery condition), or misled
+          the user into damaging the hardware (undocking or ejecting
+          the bay while buses are still active), etc.
+
+          LED control on the ThinkPad is write-only (with very few
+          exceptions on very ancient models), which makes it
+          impossible to know beforehand if important information will
+          be lost when one changes LED state.
+
+          Users that know what they are doing can enable this option
+          and the driver will allow control of every LED, including
+          the ones on the dock stations.
+
+          Never enable this option on a distribution kernel.
+
+          Say N here, unless you are building a kernel for your own
+          use, and need to control the important firmware LEDs.
+
 config THINKPAD_ACPI_DOCK
         bool "Legacy Docking Station Support"
         depends on THINKPAD_ACPI