thinkpad-acpi: hotkey event driver update

Update the HKEY event driver to:

1. Handle better the second-gen firmware, which has no HKEY mask
   support but does report FN+F3, FN+F4 and FN+F12 without the need
   for NVRAM polling.

   a) always make the mask-related attributes available in sysfs;
   b) use DMI quirks to detect the second-gen firmware;
   c) properly report that FN+F3, FN+F4 and FN+F12 are enabled,
      and available even on mask-less second-gen firmware;

2. Decouple the issuing of hotkey events towards userspace from
   their reception from the firmware.  ALSA mixer and brightness
   event reporting support will need this feature.

3. Clean up the mess in the hotkey driver a great deal.  It is
   still very convoluted, and wants a full refactoring into a
   proper event API interface, but that is not going to happen
   today.

4. Fully reset firmware interface on resume (restore hotkey
   mask and status).

5. Stop losing polled events for no good reason when changing the
   mask and poll frequencies.  We will still lose them when the
   hotkey_source_mask is changed, as well as any that happened
   between driver suspend and driver resume.

The hotkey subdriver now has the notion of user-space-visible hotkey
event mask, as well as of the set of "hotkey" events the driver needs
(because brightness/volume change reports are not just keypress
reports in most ThinkPad models).

With this rewrite, the ABI level is bumped to 0x020500 should
userspace need to know it is dealing with the updated hotkey
subdriver.

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

Documentation/laptops/thinkpad-acpi.txt

@@ -199,18 +199,22 @@ kind to allow it (and it often doesn't!).
 
 Not all bits in the mask can be modified.  Not all bits that can be
 modified do anything.  Not all hot keys can be individually controlled
-by the mask.  Some models do not support the mask at all, and in those
-models, hot keys cannot be controlled individually.  The behaviour of
-the mask is, therefore, highly dependent on the ThinkPad model.
+by the mask.  Some models do not support the mask at all.  The behaviour
+of the mask is, therefore, highly dependent on the ThinkPad model.
+
+The driver will filter out any unmasked hotkeys, so even if the firmware
+doesn't allow disabling an specific hotkey, the driver will not report
+events for unmasked hotkeys.
 
 Note that unmasking some keys prevents their default behavior.  For
 example, if Fn+F5 is unmasked, that key will no longer enable/disable
-Bluetooth by itself.
+Bluetooth by itself in firmware.
 
-Note also that not all Fn key combinations are supported through ACPI.
-For example, on the X40, the brightness, volume and "Access IBM" buttons
-do not generate ACPI events even with this driver.  They *can* be used
-through the "ThinkPad Buttons" utility, see http://www.nongnu.org/tpb/
+Note also that not all Fn key combinations are supported through ACPI
+depending on the ThinkPad model and firmware version.  On those
+ThinkPads, it is still possible to support some extra hotkeys by
+polling the "CMOS NVRAM" at least 10 times per second.  The driver
+attempts to enables this functionality automatically when required.
 
 procfs notes:
 
@@ -255,18 +259,11 @@ sysfs notes:
 		1: does nothing
 
 	hotkey_mask:
-		bit mask to enable driver-handling (and depending on
+		bit mask to enable reporting (and depending on
 		the firmware, ACPI event generation) for each hot key
 		(see above).  Returns the current status of the hot keys
 		mask, and allows one to modify it.
 
-		Note: when NVRAM polling is active, the firmware mask
-		will be different from the value returned by
-		hotkey_mask.  The driver will retain enabled bits for
-		hotkeys that are under NVRAM polling even if the
-		firmware refuses them, and will not set these bits on
-		the firmware hot key mask.
-
 	hotkey_all_mask:
 		bit mask that should enable event reporting for all
 		supported hot keys, when echoed to hotkey_mask above.
@@ -279,17 +276,19 @@ sysfs notes:
 		bit mask that should enable event reporting for all
 		supported hot keys, except those which are always
 		handled by the firmware anyway.  Echo it to
-		hotkey_mask above, to use.
+		hotkey_mask above, to use.  This is the default mask
+		used by the driver.
 
 	hotkey_source_mask:
 		bit mask that selects which hot keys will the driver
 		poll the NVRAM for.  This is auto-detected by the driver
 		based on the capabilities reported by the ACPI firmware,
 		but it can be overridden at runtime.
 
-		Hot keys whose bits are set in both hotkey_source_mask
-		and also on hotkey_mask are polled for in NVRAM.  Only a
-		few hot keys are available through CMOS NVRAM polling.
+		Hot keys whose bits are set in hotkey_source_mask are
+		polled for in NVRAM, and reported as hotkey events if
+		enabled in hotkey_mask.  Only a few hot keys are
+		available through CMOS NVRAM polling.
 
 		Warning: when in NVRAM mode, the volume up/down/mute
 		keys are synthesized according to changes in the mixer,
@@ -621,6 +620,8 @@ For Lenovo models *with* ACPI backlight control:
 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).
+   The driver will do this automatically if it detects that ACPI video
+   has been disabled.
 
 
 Bluetooth
@@ -1459,3 +1460,8 @@ Sysfs interface changelog:
 0x020400:	Marker for 16 LEDs support.  Also, LEDs that are known
 		to not exist in a given model are not registered with
 		the LED sysfs class anymore.
+
+0x020500:	Updated hotkey driver, hotkey_mask is always available
+		and it is always able to disable hot keys.  Very old
+		thinkpads are properly supported.  hotkey_bios_mask
+		is deprecated and marked for removal.