wiegand: add Wiegand bus driver

Add a bus driver for Wiegand protocol. The bus driver handles
Wiegand controller and Wiegand device managemement and driver
matching. The bus driver defines the structures for Wiegand
controllers and Wiegand devices.

Wiegand controller structure represents a master and contains
attributes such as the payload_len for configuring the size
of a single Wiegand message in bits. It also stores the
controller attributes defined in the devicetree.

Each Wiegand controller should be associated with one Wiegand
device, as Wiegand is typically a point-to-point bus.

Signed-off-by: Martin Zaťovič <m.zatovic1@gmail.com>

MAINTAINERS

@@ -22432,6 +22432,8 @@ WIEGAND BUS DRIVER
 M:	Martin Zaťovič <m.zatovic1@gmail.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/wiegand/wiegand-controller.yaml
+F:	drivers/wiegand/wiegand.c
+F:	include/linux/wiegand.h
 
 WILOCITY WIL6210 WIRELESS DRIVER
 L:	linux-wireless@vger.kernel.org

drivers/Kconfig

@@ -67,6 +67,8 @@ source "drivers/spi/Kconfig"
 
 source "drivers/spmi/Kconfig"
 
+source "drivers/wiegand/Kconfig"
+
 source "drivers/hsi/Kconfig"
 
 source "drivers/pps/Kconfig"

drivers/Makefile

@@ -146,6 +146,7 @@ obj-$(CONFIG_VHOST_RING)	+= vhost/
 obj-$(CONFIG_VHOST_IOTLB)	+= vhost/
 obj-$(CONFIG_VHOST)		+= vhost/
 obj-$(CONFIG_VLYNQ)		+= vlynq/
+obj-$(CONFIG_WIEGAND)		+= wiegand/
 obj-$(CONFIG_GREYBUS)		+= greybus/
 obj-$(CONFIG_COMEDI)		+= comedi/
 obj-$(CONFIG_STAGING)		+= staging/

drivers/wiegand/Kconfig

@@ -0,0 +1,20 @@
+config WIEGAND
+        tristate "Wiegand Bus driver"
+        help
+	  The "Wiegand Interface" is an asynchronous low-level protocol
+	  or wiring standard. It is typically used for point-to-point
+	  communication. The data length of Wiegand messages is not defined,
+	  so the devices usually default to 26, 36 or 37 bits per message.
+	  The throughput of Wiegand depends on the selected pulse length and
+	  the intervals between pulses, in comparison to other busses it
+	  is generally rather slow.
+
+	  Despite its higher age, Wiegand remains widely used in access
+	  control systems to connect a card swipe mechanism. Such mechanisms
+	  utilize the Wiegand effect to transfer data from the card to
+	  the reader.
+
+	  Wiegand uses two wires to transmit the data D0 and D1. Both lines
+	  are initially pulled up. When a bit of value 0 is being transmitted,
+	  the D0 line is pulled down. Similarly, when a bit of value 1 is being
+	  transmitted, the D1 line is pulled down.

drivers/wiegand/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_WIEGAND)			+= wiegand.o