mfd: Versatile Express config infrastructure

Versatile Express platform has an elaborated configuration system,
consisting of microcontrollers residing on the mother- and
daughterboards known as Motherboard/Daughterboard Configuration
Controller (MCC and DCC). The controllers are responsible for
the platform initialization (reset generation, flash programming,
FPGA bitfiles loading etc.) but also control clock generators,
voltage regulators, gather environmental data like temperature,
power consumption etc. Even the video output switch (FPGA) is
controlled that way.

Those devices are _not_ visible in the main address space and
the usual communication channel uses some kind of a bridge in
the peripheral block sending commands (requests) to the
controllers and receiving responses. It can take up to
500 microseconds for a transaction to be completed, therefore
it is important to provide a non-blocking interface to it.

This patch adds an abstraction of this infrastructure. Bridge
drivers can register themselves with the framework. Then,
a driver of a device can request an abstract "function" - the
request will be redirected to a bridge referred by thedd
"arm,vexpress,config-bridge" property of the device tree node.

Signed-off-by: Pawel Moll <pawel.moll@arm.com>

Documentation/devicetree/bindings/arm/vexpress.txt

@@ -11,6 +11,10 @@ the motherboard file using a /include/ directive. As the motherboard
 can be initialized in one of two different configurations ("memory
 maps"), care must be taken to include the correct one.
 
+
+Root node
+---------
+
 Required properties in the root node:
 - compatible value:
 	compatible = "arm,vexpress,<model>", "arm,vexpress";
@@ -45,6 +49,10 @@ Optional properties in the root node:
   - Coretile Express A9x4 (V2P-CA9) HBI-0225:
 	arm,hbi = <0x225>;
 
+
+CPU nodes
+---------
+
 Top-level standard "cpus" node is required. It must contain a node
 with device_type = "cpu" property for every available core, eg.:
 
@@ -59,6 +67,52 @@ with device_type = "cpu" property for every available core, eg.:
 		};
 	};
 
+
+Configuration infrastructure
+----------------------------
+
+The platform has an elaborated configuration system, consisting of
+microcontrollers residing on the mother- and daughterboards known
+as Motherboard/Daughterboard Configuration Controller (MCC and DCC).
+The controllers are responsible for the platform initialization
+(reset generation, flash programming, FPGA bitfiles loading etc.)
+but also control clock generators, voltage regulators, gather
+environmental data like temperature, power consumption etc. Even
+the video output switch (FPGA) is controlled that way.
+
+Nodes describing devices controlled by this infrastructure should
+point at the bridge device node:
+- bridge phandle:
+	arm,vexpress,config-bridge = <phandle>;
+This property can be also defined in a parent node (eg. for a DCC)
+and is effective for all children.
+
+
+Platform topology
+-----------------
+
+As Versatile Express can be configured in number of physically
+different setups, the device tree should describe platform topology.
+Root node and main motherboard node must define the following
+property, describing physical location of the children nodes:
+- site number:
+	arm,vexpress,site = <number>;
+  where 0 means motherboard, 1 or 2 are daugtherboard sites,
+  0xf means "master" site (site containing main CPU tile)
+- when daughterboards are stacked on one site, their position
+  in the stack be be described with:
+	arm,vexpress,position = <number>;
+- when describing tiles consisting more than one DCC, its number
+  can be described with:
+	arm,vexpress,dcc = <number>;
+
+Any of the numbers above defaults to zero if not defined in
+the node or any of its parent.
+
+
+Motherboard
+-----------
+
 The motherboard description file provides a single "motherboard" node
 using 2 address cells corresponding to the Static Memory Bus used
 between the motherboard and the tile. The first cell defines the Chip
@@ -96,13 +150,16 @@ The tile description must define "ranges", "interrupt-map-mask" and
 "interrupt-map" properties to translate the motherboard's address
 and interrupt space into one used by the tile's processor.
 
-Abbreviated example:
+
+Example of a VE tile description (simplified)
+---------------------------------------------
 
 /dts-v1/;
 
 / {
 	model = "V2P-CA5s";
 	arm,hbi = <0x225>;
+	arm,vexpress,site = <0xf>;
 	compatible = "arm,vexpress-v2p-ca5s", "arm,vexpress";
 	interrupt-parent = <&gic>;
 	#address-cells = <1>;
@@ -134,6 +191,15 @@ Abbreviated example:
 		      <0x2c000100 0x100>;
 	};
 
+	dcc {
+		compatible = "simple-bus";
+		arm,vexpress,config-bridge = <&v2m_sysreg>;
+
+		osc@0 {
+			compatible = "arm,vexpress-osc";
+		};
+	};
+
 	motherboard {
 		/* CS0 is visible at 0x08000000 */
 		ranges = <0 0 0x08000000 0x04000000>;

drivers/mfd/Kconfig

@@ -1070,3 +1070,9 @@ config MCP_UCB1200_TS
 	depends on MCP_UCB1200 && INPUT
 
 endmenu
+
+config VEXPRESS_CONFIG
+	bool
+	help
+	  Platform configuration infrastructure for the ARM Ltd.
+	  Versatile Express.

drivers/mfd/Makefile

@@ -138,3 +138,4 @@ obj-$(CONFIG_MFD_RC5T583)	+= rc5t583.o rc5t583-irq.o
 obj-$(CONFIG_MFD_SEC_CORE)	+= sec-core.o sec-irq.o
 obj-$(CONFIG_MFD_SYSCON)	+= syscon.o
 obj-$(CONFIG_MFD_LM3533)	+= lm3533-core.o lm3533-ctrlbank.o
+obj-$(CONFIG_VEXPRESS_CONFIG)	+= vexpress-config.o