On hardware with limited gpios one column select gpio can select
two different rows when using some additional hardware logic:
high value selects one row, low value selects another row. Add
support for such matrix keyboards and document device tree
bindings used to describe them.

Since half of the columns is always not selected, interrupts won't be
generated for press events on these columns. To generate interrupts
for not selected columns we need to periodicaly switch to these columns
in order to catch the potential press events. This is done by additional
work function.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
---
v2:
 - do not use inline attribute for matrix_keyboard_row_events(),
   it causes reporting wrong events for some keys if the kernel
   was built using gcc 4.7.2.

 .../bindings/input/gpio-matrix-keypad.txt          |    7 ++
 drivers/input/keyboard/matrix_keypad.c             |  112 ++++++++++++++++----
 include/linux/input/matrix_keypad.h                |    6 +
 3 files changed, 106 insertions(+), 19 deletions(-)

diff --git a/Documentation/devicetree/bindings/input/gpio-matrix-keypad.txt b/Documentation/devicetree/bindings/input/gpio-matrix-keypad.txt
index ead641c..57f4be3 100644
--- a/Documentation/devicetree/bindings/input/gpio-matrix-keypad.txt
+++ b/Documentation/devicetree/bindings/input/gpio-matrix-keypad.txt

@@ -23,6 +23,13 @@ Optional Properties:
 - debounce-delay-ms:   debounce interval in milliseconds
 - col-scan-delay-us:   delay, measured in microseconds, that is needed
                        before we can scan keypad after activating column gpio
+- col-gpios-binary:    specify that high and low states of a column gpio
+                       select two different rows (boards with limited gpios
+                       could support this by additional hardware logic)
+- col-switch-delay-ms: column gpio switch interval for selecting alternative
+                       rows when using 'col-gpios-binary'. This is needed for
+                       periodical selecting of the alternative rows to be able
+                       to generate keypad interrupts for them