siox: new driver framework for eckelmann SIOX

SIOX is a bus system invented at Eckelmann AG to control their building
management and refrigeration systems. Traditionally the bus was
implemented on custom microcontrollers, today Linux based machines are
in use, too.

The topology on a SIOX bus looks as follows:

      ,------->--DCLK-->---------------+----------------------.
      ^                                v                      v
 ,--------.                ,----------------------.       ,------
 |        |                |   ,--------------.   |       |
 |        |--->--DOUT-->---|->-|shift register|->-|--->---|
 |        |                |   `--------------'   |       |
 | master |                |        device        |       |  device
 |        |                |   ,--------------.   |       |
 |        |---<--DIN---<---|-<-|shift register|-<-|---<---|
 |        |                |   `--------------'   |       |
 `--------'                `----------------------'       `------
      v                                ^                      ^
      `----------DLD-------------------+----------------------'

There are two control lines (DCLK and DLD) driven from the bus master to
all devices in parallel and two daisy chained data lines, one for input
and one for output. DCLK is the clock to shift both chains by a single
bit. On an edge of DLD the devices latch both their input and output
shift registers.

This patch adds a framework for this bus type.

Acked-by: Gavin Schenk <g.schenk@eckelmann.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Uwe Kleine-König

Documentation/ABI/testing/sysfs-bus-siox

@@ -0,0 +1,87 @@
+What:		/sys/bus/siox/devices/siox-X/active
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		On reading represents the current state of the bus. If it
+		contains a "0" the bus is stopped and connected devices are
+		expected to not do anything because their watchdog triggered.
+		When the file contains a "1" the bus is operated and periodically
+		does a push-pull cycle to write and read data from the
+		connected devices.
+		When writing a "0" or "1" the bus moves to the described state.
+
+What:		/sys/bus/siox/devices/siox-X/device_add
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Write-only file. Write
+
+			<type> <inbytes> <outbytes> <statustype>
+
+		to add a new device dynamically. <type> is the name that is used to match
+		to a driver (similar to the platform bus). <inbytes> and <outbytes> define
+		the length of the input and output shift register in bytes respectively.
+		<statustype> defines the 4 bit device type that is check to identify connection
+		problems.
+		The new device is added to the end of the existing chain.
+
+What:		/sys/bus/siox/devices/siox-X/device_remove
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Write-only file. A single write removes the last device in the siox chain.
+
+What:		/sys/bus/siox/devices/siox-X/poll_interval_ns
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Defines the interval between two poll cycles in nano seconds.
+		Note this is rounded to jiffies on writing. On reading the current value
+		is returned.
+
+What:		/sys/bus/siox/devices/siox-X-Y/connected
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value. "0" means the Yth device on siox bus X isn't "connected" i.e.
+		communication with it is not ensured. "1" signals a working connection.
+
+What:		/sys/bus/siox/devices/siox-X-Y/inbytes
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the inbytes value provided to siox-X/device_add
+
+What:		/sys/bus/siox/devices/siox-X-Y/status_errors
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Counts the number of time intervals when the read status byte doesn't yield the
+		expected value.
+
+What:		/sys/bus/siox/devices/siox-X-Y/type
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the type value provided to siox-X/device_add.
+
+What:		/sys/bus/siox/devices/siox-X-Y/watchdog
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting if the watchdog of the siox device is
+		active. "0" means the watchdog is not active and the device is expected to
+		be operational. "1" means the watchdog keeps the device in reset.
+
+What:		/sys/bus/siox/devices/siox-X-Y/watchdog_errors
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the number to time intervals when the
+		watchdog was active.
+
+What:		/sys/bus/siox/devices/siox-X-Y/outbytes
+KernelVersion:	4.16
+Contact:	Gavin Schenk <g.schenk@eckelmann.de>, Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Description:
+		Read-only value reporting the outbytes value provided to siox-X/device_add.

drivers/Kconfig

@@ -211,4 +211,6 @@ source "drivers/mux/Kconfig"
 
 source "drivers/opp/Kconfig"
 
+source "drivers/siox/Kconfig"
+
 endmenu

drivers/Makefile

@@ -184,3 +184,4 @@ obj-$(CONFIG_FPGA)		+= fpga/
 obj-$(CONFIG_FSI)		+= fsi/
 obj-$(CONFIG_TEE)		+= tee/
 obj-$(CONFIG_MULTIPLEXER)	+= mux/
+obj-$(CONFIG_SIOX)		+= siox/

drivers/siox/Kconfig

@@ -0,0 +1,9 @@
+menuconfig SIOX
+	tristate "Eckelmann SIOX Support"
+	help
+	  SIOX stands for Serial Input Output eXtension and is a synchronous
+	  bus system invented by Eckelmann AG. It is used in their control and
+	  remote monitoring systems for commercial and industrial refrigeration
+	  to drive additional I/O units.
+
+	  Unless you know better, it is probably safe to say "no" here.

drivers/siox/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_SIOX) += siox-core.o