ACPI: thinkpad-acpi: add CMOS NVRAM polling for hot keys (v9)

Older ThinkPad models do not export some of the hot keys over the
event-based ACPI hot key interface.  For these models, one has to poll
the CMOS NVRAM to check the key state at a rate faster than the expected
rate at which the user might repeatedly press the same hot key.

This patch implements this functionality for many of the hotkeys in a
transparent way: hot keys will now Just Work, and the driver knows the
best approach (events or NVRAM polling) to employ, based on the
HKEY.MHKA ACPI method.

Also, the driver can turn off the polling when there are no users for
the hot keys that need such polling.

The NVRAM-based hot keys of the A3x series that have never been
implemented by later models are not supported, to avoid changes in the
keymap of the input devices that could cause headaches in the future.

There is a Kconfig option to avoid compiling the NVRAM polling code, as
it is not very small, and unlikely to be useful on any ThinkPad newer
than a T40, X31 or R52.

This feature is based on a previous effort by Richard Hughes.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index b5e67c0ff43..b1f9a405c82 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -219,6 +219,25 @@ config THINKPAD_ACPI_BAY
 
 	  If you are not sure, say Y here.
 
+config THINKPAD_ACPI_HOTKEY_POLL
+	bool "Suport NVRAM polling for hot keys"
+	depends on THINKPAD_ACPI
+	default y
+	---help---
+	  Some thinkpad models benefit from NVRAM polling to detect a few of
+	  the hot key press events.  If you know your ThinkPad model does not
+	  need to do NVRAM polling to support any of the hot keys you use,
+	  unselecting this option will save about 1kB of memory.
+
+	  ThinkPads T40 and newer, R52 and newer, and X31 and newer are
+	  unlikely to need NVRAM polling in their latest BIOS versions.
+
+	  NVRAM polling can detect at most the following keys: ThinkPad/Access
+	  IBM, Zoom, Switch Display (fn+F7), ThinkLight, Volume up/down/mute,
+	  Brightness up/down, Display Expand (fn+F8), Hibernate (fn+F12).
+
+	  If you are not sure, say Y here.  The driver enables polling only if
+	  it is strictly necessary to do so.
 
 config ATMEL_SSC
 	tristate "Device driver for Atmel SSC peripheral"