with hotkey_report_mode.
 
 
+Brightness hotkey notes:
+
+These are the current sane choices for brightness key mapping in
+thinkpad-acpi:
+
+For IBM and Lenovo models *without* ACPI backlight control (the ones on
+which thinkpad-acpi will autoload its backlight interface by default,
+and on which ACPI video does not export a backlight interface):
+
+1. Don't enable or map the brightness hotkeys in thinkpad-acpi, as
+   these older firmware versions unfortunately won't respect the hotkey
+   mask for brightness keys anyway, and always reacts to them.  This
+   usually work fine, unless X.org drivers are doing something to block
+   the BIOS.  In that case, use (3) below.  This is the default mode of
+   operation.
+
+2. Enable the hotkeys, but map them to something else that is NOT
+   KEY_BRIGHTNESS_UP/DOWN or any other keycode that would cause
+   userspace to try to change the backlight level, and use that as an
+   on-screen-display hint.
+
+3. IF AND ONLY IF X.org drivers find a way to block the firmware from
+   automatically changing the brightness, enable the hotkeys and map
+   them to KEY_BRIGHTNESS_UP and KEY_BRIGHTNESS_DOWN, and feed that to
+   something that calls xbacklight.  thinkpad-acpi will not be able to
+   change brightness in that case either, so you should disable its
+   backlight interface.
+
+For Lenovo models *with* ACPI backlight control:
+
+1. Load up ACPI video and use that.  ACPI video will report ACPI
+   events for brightness change keys.  Do not mess with thinkpad-acpi
+   defaults in this case.  thinkpad-acpi should not have anything to do
+   with backlight events in a scenario where ACPI video is loaded:
+   brightness hotkeys must be disabled, and the backlight interface is
+   to be kept disabled as well.  This is the default mode of operation.
+
+2. Do *NOT* load up ACPI video, enable the hotkeys in thinkpad-acpi,
+   and map them to KEY_BRIGHTNESS_UP and KEY_BRIGHTNESS_DOWN.  Process
+   these keys on userspace somehow (e.g. by calling xbacklight).
+
 Bluetooth
 ---------
 
                dim the display.
 
 
+WARNING:
+
+    Whatever you do, do NOT ever call thinkpad-acpi backlight-level change
+    interface and the ACPI-based backlight level change interface
+    (available on newer BIOSes, and driven by the Linux ACPI video driver)
+    at the same time.  The two will interact in bad ways, do funny things,
+    and maybe reduce the life of the backlight lamps by needlessly kicking
+    its level up and down at every change.
+
 Volume control -- /proc/acpi/ibm/volume
 ---------------------------------------
 
 
        u32 light:1;
        u32 light_status:1;
        u32 bright_16levels:1;
+       u32 bright_acpimode:1;
        u32 wan:1;
        u32 fan_ctrl_status_undef:1;
        u32 input_device_registered:1;
        return 0;
 }
 
+static int __init tpacpi_query_bcl_levels(acpi_handle handle)
+{
+       struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+       union acpi_object *obj;
+       int rc;
+
+       if (ACPI_SUCCESS(acpi_evaluate_object(handle, NULL, NULL, &buffer))) {
+               obj = (union acpi_object *)buffer.pointer;
+               if (!obj || (obj->type != ACPI_TYPE_PACKAGE)) {
+                       printk(TPACPI_ERR "Unknown _BCL data, "
+                              "please report this to %s\n", TPACPI_MAIL);
+                       rc = 0;
+               } else {
+                       rc = obj->package.count;
+               }
+       } else {
+               return 0;
+       }
+
+       kfree(buffer.pointer);
+       return rc;
+}
+
+static acpi_status __init tpacpi_acpi_walk_find_bcl(acpi_handle handle,
+                                       u32 lvl, void *context, void **rv)
+{
+       char name[ACPI_PATH_SEGMENT_LENGTH];
+       struct acpi_buffer buffer = { sizeof(name), &name };
+
+       if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_SINGLE_NAME, &buffer)) &&
+           !strncmp("_BCL", name, sizeof(name) - 1)) {
+               BUG_ON(!rv || !*rv);
+               **(int **)rv = tpacpi_query_bcl_levels(handle);
+               return AE_CTRL_TERMINATE;
+       } else {
+               return AE_OK;
+       }
+}
+
+/*
+ * Returns 0 (no ACPI _BCL or _BCL invalid), or size of brightness map
+ */
+static int __init tpacpi_check_std_acpi_brightness_support(void)
+{
+       int status;
+       int bcl_levels = 0;
+       void *bcl_ptr = &bcl_levels;
+
+       if (!vid_handle) {
+               TPACPI_ACPIHANDLE_INIT(vid);
+       }
+       if (!vid_handle)
+               return 0;
+
+       /*
+        * Search for a _BCL method, and execute it.  This is safe on all
+        * ThinkPads, and as a side-effect, _BCL will place a Lenovo Vista
+        * BIOS in ACPI backlight control mode.  We do NOT have to care
+        * about calling the _BCL method in an enabled video device, any
+        * will do for our purposes.
+        */
+
+       status = acpi_walk_namespace(ACPI_TYPE_METHOD, vid_handle, 3,
+                                    tpacpi_acpi_walk_find_bcl, NULL,
+                                    &bcl_ptr);
+
+       if (ACPI_SUCCESS(status) && bcl_levels > 2) {
+               tp_features.bright_acpimode = 1;
+               return (bcl_levels - 2);
+       }
+
+       return 0;
+}
+
 /*************************************************************************
  * thinkpad-acpi driver attributes
  */
                KEY_UNKNOWN,    /* 0x0D: FN+INSERT */
                KEY_UNKNOWN,    /* 0x0E: FN+DELETE */
 
+               /* These either have to go through ACPI video, or
+                * act like in the IBM ThinkPads, so don't ever
+                * enable them by default */
                KEY_RESERVED,   /* 0x0F: FN+HOME (brightness up) */
                KEY_RESERVED,   /* 0x10: FN+END (brightness down) */
 
                        set_bit(SW_TABLET_MODE, tpacpi_inputdev->swbit);
                }
 
+               /* Do not issue duplicate brightness change events to
+                * userspace */
+               if (!tp_features.bright_acpimode)
+                       /* update bright_acpimode... */
+                       tpacpi_check_std_acpi_brightness_support();
+
+               if (tp_features.bright_acpimode) {
+                       printk(TPACPI_INFO
+                              "This ThinkPad has standard ACPI backlight "
+                              "brightness control, supported by the ACPI "
+                              "video driver\n");
+                       printk(TPACPI_NOTICE
+                              "Disabling thinkpad-acpi brightness events "
+                              "by default...\n");
+
+                       /* The hotkey_reserved_mask change below is not
+                        * necessary while the keys are at KEY_RESERVED in the
+                        * default map, but better safe than sorry, leave it
+                        * here as a marker of what we have to do, especially
+                        * when we finally become able to set this at runtime
+                        * on response to X.org requests */
+                       hotkey_reserved_mask |=
+                               (1 << TP_ACPI_HOTKEYSCAN_FNHOME)
+                               | (1 << TP_ACPI_HOTKEYSCAN_FNEND);
+               }
+
                dbg_printk(TPACPI_DBG_INIT,
                                "enabling hot key handling\n");
                res = hotkey_status_set(1);
 
 /* --------------------------------------------------------------------- */
 
-static int __init tpacpi_query_bcll_levels(acpi_handle handle)
-{
-       struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
-       union acpi_object *obj;
-       int rc;
-
-       if (ACPI_SUCCESS(acpi_evaluate_object(handle, NULL, NULL, &buffer))) {
-               obj = (union acpi_object *)buffer.pointer;
-               if (!obj || (obj->type != ACPI_TYPE_PACKAGE)) {
-                       printk(TPACPI_ERR "Unknown BCLL data, "
-                              "please report this to %s\n", TPACPI_MAIL);
-                       rc = 0;
-               } else {
-                       rc = obj->package.count;
-               }
-       } else {
-               return 0;
-       }
-
-       kfree(buffer.pointer);
-       return rc;
-}
-
-static acpi_status __init brightness_find_bcll(acpi_handle handle, u32 lvl,
-                                       void *context, void **rv)
-{
-       char name[ACPI_PATH_SEGMENT_LENGTH];
-       struct acpi_buffer buffer = { sizeof(name), &name };
-
-       if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_SINGLE_NAME, &buffer)) &&
-           !strncmp("BCLL", name, sizeof(name) - 1)) {
-               if (tpacpi_query_bcll_levels(handle) == 16) {
-                       *rv = handle;
-                       return AE_CTRL_TERMINATE;
-               } else {
-                       return AE_OK;
-               }
-       } else {
-               return AE_OK;
-       }
-}
-
-static int __init brightness_check_levels(void)
-{
-       int status;
-       void *found_node = NULL;
-
-       if (!vid_handle) {
-               TPACPI_ACPIHANDLE_INIT(vid);
-       }
-       if (!vid_handle)
-               return 0;
-
-       /* Search for a BCLL package with 16 levels */
-       status = acpi_walk_namespace(ACPI_TYPE_PACKAGE, vid_handle, 3,
-                                       brightness_find_bcll, NULL,
-                                       &found_node);
-
-       return (ACPI_SUCCESS(status) && found_node != NULL);
-}
-
-static acpi_status __init brightness_find_bcl(acpi_handle handle, u32 lvl,
-                                       void *context, void **rv)
-{
-       char name[ACPI_PATH_SEGMENT_LENGTH];
-       struct acpi_buffer buffer = { sizeof(name), &name };
-
-       if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_SINGLE_NAME, &buffer)) &&
-           !strncmp("_BCL", name, sizeof(name) - 1)) {
-               *rv = handle;
-               return AE_CTRL_TERMINATE;
-       } else {
-               return AE_OK;
-       }
-}
-
-static int __init brightness_check_std_acpi_support(void)
-{
-       int status;
-       void *found_node = NULL;
-
-       if (!vid_handle) {
-               TPACPI_ACPIHANDLE_INIT(vid);
-       }
-       if (!vid_handle)
-               return 0;
-
-       /* Search for a _BCL method, but don't execute it */
-       status = acpi_walk_namespace(ACPI_TYPE_METHOD, vid_handle, 3,
-                                    brightness_find_bcl, NULL, &found_node);
-
-       return (ACPI_SUCCESS(status) && found_node != NULL);
-}
-
 static int __init brightness_init(struct ibm_init_struct *iibm)
 {
        int b;
 
        mutex_init(&brightness_mutex);
 
-       if (!brightness_enable) {
-               dbg_printk(TPACPI_DBG_INIT,
-                          "brightness support disabled by "
-                          "module parameter\n");
-               return 1;
-       } else if (brightness_enable > 1) {
-               if (brightness_check_std_acpi_support()) {
+       /*
+        * We always attempt to detect acpi support, so as to switch
+        * Lenovo Vista BIOS to ACPI brightness mode even if we are not
+        * going to publish a backlight interface
+        */
+       b = tpacpi_check_std_acpi_brightness_support();
+       if (b > 0) {
+               if (thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO) {
+                       printk(TPACPI_NOTICE
+                              "Lenovo BIOS switched to ACPI backlight "
+                              "control mode\n");
+               }
+               if (brightness_enable > 1) {
                        printk(TPACPI_NOTICE
                               "standard ACPI backlight interface "
                               "available, not loading native one...\n");
                }
        }
 
+       if (!brightness_enable) {
+               dbg_printk(TPACPI_DBG_INIT,
+                          "brightness support disabled by "
+                          "module parameter\n");
+               return 1;
+       }
+
+       if (b > 16) {
+               printk(TPACPI_ERR
+                      "Unsupported brightness interface, "
+                      "please contact %s\n", TPACPI_MAIL);
+               return 1;
+       }
+       if (b == 16)
+               tp_features.bright_16levels = 1;
+
        if (!brightness_mode) {
                if (thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO)
                        brightness_mode = 2;
        if (brightness_mode > 3)
                return -EINVAL;
 
-       tp_features.bright_16levels =
-                       thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO &&
-                       brightness_check_levels();
-
        b = brightness_get(NULL);
        if (b < 0)
                return 1;