mfd: dt: Add Aspeed Low Pin Count Controller bindings

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/aspeed-lpc.txt

+======================================================================
+Device tree bindings for the Aspeed Low Pin Count (LPC) Bus Controller
+======================================================================
+
+The LPC bus is a means to bridge a host CPU to a number of low-bandwidth
+peripheral devices, replacing the use of the ISA bus in the age of PCI[0]. The
+primary use case of the Aspeed LPC controller is as a slave on the bus
+(typically in a Baseboard Management Controller SoC), but under certain
+conditions it can also take the role of bus master.
+
+The LPC controller is represented as a multi-function device to account for the
+mix of functionality it provides. The principle split is between the register
+layout at the start of the I/O space which is, to quote the Aspeed datasheet,
+"basically compatible with the [LPC registers from the] popular BMC controller
+H8S/2168[1]", and everything else, where everything else is an eclectic
+collection of functions with a esoteric register layout. "Everything else",
+here labeled the "host" portion of the controller, includes, but is not limited
+to:
+
+* An IPMI Block Transfer[2] Controller
+
+* An LPC Host Controller: Manages LPC functions such as host vs slave mode, the
+  physical properties of some LPC pins, configuration of serial IRQs, and
+  APB-to-LPC bridging amonst other functions.
+
+* An LPC Host Interface Controller: Manages functions exposed to the host such
+  as LPC firmware hub cycles, configuration of the LPC-to-AHB mapping, UART
+  management and bus snoop configuration.
+
+* A set of SuperIO[3] scratch registers: Enables implementation of e.g. custom
+  hardware management protocols for handover between the host and baseboard
+  management controller.
+
+Additionally the state of the LPC controller influences the pinmux
+configuration, therefore the host portion of the controller is exposed as a
+syscon as a means to arbitrate access.
+
+[0] http://www.intel.com/design/chipsets/industry/25128901.pdf
+[1] https://www.renesas.com/en-sg/doc/products/mpumcu/001/rej09b0078_h8s2168.pdf?key=7c88837454702128622bee53acbda8f4
+[2] http://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/ipmi-second-gen-interface-spec-v2-rev1-1.pdf
+[3] https://en.wikipedia.org/wiki/Super_I/O
+
+Required properties
+===================
+
+- compatible:	One of:
+		"aspeed,ast2400-lpc", "simple-mfd"
+		"aspeed,ast2500-lpc", "simple-mfd"
+
+- reg:		contains the physical address and length values of the Aspeed
+                LPC memory region.
+
+- #address-cells: <1>
+- #size-cells:	<1>
+- ranges: 	Maps 0 to the physical address and length of the LPC memory
+                region
+
+Required LPC Child nodes
+========================
+
+BMC Node
+--------
+
+- compatible:	One of:
+		"aspeed,ast2400-lpc-bmc"
+		"aspeed,ast2500-lpc-bmc"
+
+- reg:		contains the physical address and length values of the
+                H8S/2168-compatible LPC controller memory region
+
+Host Node
+---------
+
+- compatible:   One of:
+		"aspeed,ast2400-lpc-host", "simple-mfd", "syscon"
+		"aspeed,ast2500-lpc-host", "simple-mfd", "syscon"
+
+- reg:		contains the address and length values of the host-related
+                register space for the Aspeed LPC controller
+
+- #address-cells: <1>
+- #size-cells:	<1>
+- ranges: 	Maps 0 to the address and length of the host-related LPC memory
+                region
+
+Example:
+
+lpc: lpc@1e789000 {
+	compatible = "aspeed,ast2500-lpc", "simple-mfd";
+	reg = <0x1e789000 0x1000>;
+
+	#address-cells = <1>;
+	#size-cells = <1>;
+	ranges = <0x0 0x1e789000 0x1000>;
+
+	lpc_bmc: lpc-bmc@0 {
+		compatible = "aspeed,ast2500-lpc-bmc";
+		reg = <0x0 0x80>;
+	};
+
+	lpc_host: lpc-host@80 {
+		compatible = "aspeed,ast2500-lpc-host", "simple-mfd", "syscon";
+		reg = <0x80 0x1e0>;
+		reg-io-width = <4>;
+
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges = <0x0 0x80 0x1e0>;
+	};
+};
+