====================================================================== 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>; }; }; BMC Node Children ================== Host Node Children ================== LPC Host Interface Controller ------------------- The 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. Required properties: - compatible: One of: "aspeed,ast2400-lpc-ctrl"; "aspeed,ast2500-lpc-ctrl"; - reg: contains offset/length values of the host interface controller memory regions - clocks: contains a phandle to the syscon node describing the clocks. There should then be one cell representing the clock to use Optional properties: - memory-region: A phandle to a reserved_memory region to be used for the LPC to AHB mapping - flash: A phandle to the SPI flash controller containing the flash to be exposed over the LPC to AHB mapping Example: lpc-host@80 { lpc_ctrl: lpc-ctrl@0 { compatible = "aspeed,ast2500-lpc-ctrl"; reg = <0x0 0x80>; clocks = <&syscon ASPEED_CLK_GATE_LCLK>; memory-region = <&flash_memory>; flash = <&spi>; }; }; LPC Host Controller ------------------- The Aspeed LPC Host Controller configures the Low Pin Count (LPC) bus behaviour between the host and the baseboard management controller. The registers exist in the "host" portion of the Aspeed LPC controller, which must be the parent of the LPC host controller node. Required properties: - compatible: One of: "aspeed,ast2400-lhc"; "aspeed,ast2500-lhc"; - reg: contains offset/length values of the LHC memory regions. In the AST2400 and AST2500 there are two regions. Example: lhc: lhc@20 { compatible = "aspeed,ast2500-lhc"; reg = <0x20 0x24 0x48 0x8>; }; LPC reset control ----------------- The UARTs present in the ASPEED SoC can have their resets tied to the reset state of the LPC bus. Some systems may chose to modify this configuration. Required properties: - compatible: "aspeed,ast2500-lpc-reset" or "aspeed,ast2400-lpc-reset" - reg: offset and length of the IP in the LHC memory region - #reset-controller indicates the number of reset cells expected Example: lpc_reset: reset-controller@18 { compatible = "aspeed,ast2500-lpc-reset"; reg = <0x18 0x4>; #reset-cells = <1>; };