FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/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, which 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] https://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-v2", "simple-mfd", "syscon"
                    "aspeed,ast2500-lpc-v2", "simple-mfd", "syscon"
                    "aspeed,ast2600-lpc-v2", "simple-mfd", "syscon"
    
    - 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
    
    Example:
    
    lpc: lpc@1e789000 {
            compatible = "aspeed,ast2500-lpc-v2", "simple-mfd", "syscon";
            reg = <0x1e789000 0x1000>;
    
            #address-cells = <1>;
            #size-cells = <1>;
            ranges = <0x0 0x1e789000 0x1000>;
    
            lpc_snoop: lpc-snoop@0 {
                    compatible = "aspeed,ast2600-lpc-snoop";
                    reg = <0x0 0x80>;
                    interrupts = <GIC_SPI 144 IRQ_TYPE_LEVEL_HIGH>;
                    snoop-ports = <0x80>;
            };
    };
    
    
    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";
                    "aspeed,ast2600-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_ctrl: lpc-ctrl@80 {
           compatible = "aspeed,ast2500-lpc-ctrl";
           reg = <0x80 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";
                   "aspeed,ast2600-lhc";
   
   - reg:          contains offset/length values of the LHC memory regions. In the
                   AST2400 and AST2500 there are two regions.
   
   Example:
   
   lhc: lhc@a0 {
           compatible = "aspeed,ast2500-lhc";
           reg = <0xa0 0x24 0xc8 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:          One of:
                           "aspeed,ast2600-lpc-reset";
                           "aspeed,ast2500-lpc-reset";
                           "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@98 {
           compatible = "aspeed,ast2500-lpc-reset";
           reg = <0x98 0x4>;
           #reset-cells = <1>;
   };

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