Input: PS/2 gpio bit banging driver for serio bus

This driver provides PS/2 serio bus support by implementing bit banging
with the GPIO API. The GPIO pins, data and clock, can be configured with
a node in the device tree or by generic device properties (GDP).

Writing to a device is supported as well, though it is possible timings
can not be halt as they are tough and difficult to reach with bit banging.
Therefore it can be configured (also in DT and GDP) whether the serio
write function should be available for clients.

This driver is for development purposes and not recommended for productive
use. However, this driver can be useful e.g. when no USB port is available
or using old peripherals is desired as PS/2 controller chips getting rare.

This driver was tested on bcm2825 and on Kirin 960 and it worked well
together with the atkbd and psmouse driver.
Signed-off-by: Danilo Krummrich <danilokrummrich@dk-develop.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/serio/ps2-gpio.txt

+Device-Tree binding for ps/2 gpio device
+
+Required properties:
+	- compatible = "ps2-gpio"
+	- data-gpios: the data pin
+	- clk-gpios: the clock pin
+	- interrupts: Should trigger on the falling edge of the clock line.
+
+Optional properties:
+	- write-enable: Indicates whether write function is provided
+	to serio device. Possibly providing the write fn will not work, because
+	of the tough timing requirements.
+
+Example nodes:
+
+ps2@0 {
+	compatible = "ps2-gpio";
+	interrupt-parent = <&gpio>;
+	interrupts = <23 IRQ_TYPE_EDGE_FALLING>;
+	data-gpios = <&gpio 24 GPIO_ACTIVE_HIGH>;
+	clk-gpios = <&gpio 23 GPIO_ACTIVE_HIGH>;
+	write-enable;
+};

Documentation/gpio/drivers-on-gpio.txt

@@ -84,6 +84,11 @@ hardware descriptions such as device tree or ACPI:
   NAND flash MTD subsystem and provides chip access and partition parsing like
   any other NAND driving hardware.
 
+- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
+  bus, data and clock line, by bit banging two GPIO lines. It will appear as
+  any other serio bus to the system and makes it possible to connect drivers
+  for e.g. keyboards and other PS/2 protocol based devices.
+
 Apart from this there are special GPIO drivers in subsystems like MMC/SD to
 read card detect and write protect GPIO lines, and in the TTY serial subsystem
 to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The

drivers/input/serio/Kconfig

@@ -292,6 +292,17 @@ config SERIO_SUN4I_PS2
 	  To compile this driver as a module, choose M here: the
 	  module will be called sun4i-ps2.
 
+config SERIO_GPIO_PS2
+	tristate "GPIO PS/2 bit banging driver"
+	depends on GPIOLIB
+	help
+	  Say Y here if you want PS/2 bit banging support via GPIO.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ps2-gpio.
+
+	  If you are unsure, say N.
+
 config USERIO
 	tristate "User space serio port driver support"
 	help

drivers/input/serio/Makefile

@@ -30,4 +30,5 @@ obj-$(CONFIG_SERIO_APBPS2)	+= apbps2.o
 obj-$(CONFIG_SERIO_OLPC_APSP)	+= olpc_apsp.o
 obj-$(CONFIG_HYPERV_KEYBOARD)	+= hyperv-keyboard.o
 obj-$(CONFIG_SERIO_SUN4I_PS2)	+= sun4i-ps2.o
+obj-$(CONFIG_SERIO_GPIO_PS2)	+= ps2-gpio.o
 obj-$(CONFIG_USERIO)		+= userio.o