2 files changed, 18 insertions, 6 deletions

diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index 88fc0661de56..f2ff638cce8d 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -1169,17 +1169,19 @@ may not be distinct.  Later Lenovo models that implement the ACPI
 display backlight brightness control methods have 16 levels, ranging
 from 0 to 15.
 
-There are two interfaces to the firmware for direct brightness control,
-EC and UCMS (or CMOS).  To select which one should be used, use the
-brightness_mode module parameter: brightness_mode=1 selects EC mode,
-brightness_mode=2 selects UCMS mode, brightness_mode=3 selects EC
-mode with NVRAM backing (so that brightness changes are remembered
-across shutdown/reboot).
+For IBM ThinkPads, there are two interfaces to the firmware for direct
+brightness control, EC and UCMS (or CMOS).  To select which one should be
+used, use the brightness_mode module parameter: brightness_mode=1 selects
+EC mode, brightness_mode=2 selects UCMS mode, brightness_mode=3 selects EC
+mode with NVRAM backing (so that brightness changes are remembered across
+shutdown/reboot).
 
 The driver tries to select which interface to use from a table of
 defaults for each ThinkPad model.  If it makes a wrong choice, please
 report this as a bug, so that we can fix it.
 
+Lenovo ThinkPads only support brightness_mode=2 (UCMS).
+
 When display backlight brightness controls are available through the
 standard ACPI interface, it is best to use it instead of this direct
 ThinkPad-specific interface.  The driver will disable its native
diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 5a22a064222c..c8d74dbacbbd 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -5696,6 +5696,10 @@ static struct ibm_struct ecdump_driver_data = {
  *   Bit 3-0: backlight brightness level
  *
  * brightness_get_raw returns status data in the HBRV layout
+ *
+ * WARNING: The X61 has been verified to use HBRV for something else, so
+ * this should be used _only_ on IBM ThinkPads, and maybe with some careful
+ * testing on the very early *60 Lenovo models...
  */
 
 enum {
@@ -5996,6 +6000,12 @@ static int __init brightness_init(struct ibm_init_struct *iibm)
                            brightness_mode);
         }
 
+        /* Safety */
+        if (thinkpad_id.vendor != PCI_VENDOR_ID_IBM &&
+            (brightness_mode == TPACPI_BRGHT_MODE_ECNVRAM ||
+             brightness_mode == TPACPI_BRGHT_MODE_EC))
+                return -EINVAL;
+
         if (tpacpi_brightness_get_raw(&b) < 0)
                 return 1;