1. Introduction
  1.1. Project/Component Working Name:
    New MD Nodes to Support I/O Reconfiguration for Failover Conditions.

  1.2. Name of Document Author/Supplier:
    Marc Fidler

  1.3. Date of This Document:
    05/27/2008

  1.4. Email Aliases:
       1.4.1. Responsible Manager: Chad Solomon
       1.4.2. Responsible Engineer: Marc Fidler
       1.4.3. Interest List: John Johnson

2. Project Summary
  2.1. Project Description:
    This project defines new MD nodes to represent the current and potential paths to 
    a PCIe switch when multiple IO topology configurations are possible.

3. Business Summary
  3.1. Problem Area:
    Current architecture prevents operating system boot if the PCIE device paths have 
    changed since the previous OS boot. This can happen, for example, due to a host-to-PCIE
    bridge being eliminated from the system where the PCI switches are re-routed to work
    around the missing bridge.

    This case is attempting to solve a long standing problem where I/O topology changes 
    necessitate an operating system reinstall.

4. Technical Description:
   4.1. Details:
    This project defines new MD nodes to associate all possible device paths to the upstream
    port of a PCIE switch. The operating system will use these nodes to remap existing 
    device node paths.

    Solaris uses the device node paths to configure devices. A unique device_instance 
    number is created in /dev and /etc/path_to_inst file for every I/O path.  Solaris 
    expects the I/O path to be constant.  When the same device is found at a different 
    I/O patsh after power-cycle it is treated as a new device, which can happen when a 
    node is removed or added. 

    In order for vBSC to remain stateless, there must be some mechanism to name all of
    the potential PCIe paths to a switch.

    For example, on Batoka, the switch below cpu0 can be reached with the following paths:
	/pci@400
	/pci@500/pci@0/pci@1/pci@0/pci@1
	/pci@600/pci@0/pci@1
	/pci@700/pci@0/pci@1/pci@0/pci@1/pci@0/pci@1

    When cpu0 exists, we use the first path (/pci@400) to acces the switch, and the rest 
    are aliases.  So the resulting ioalias node would be:

    node ioalias pcie0 {
        current = "/pci@400";
        aliases = "/pci@500/pci@0/pci@1/pci@0/pci@1" +
              "/pci@600/pci@0/pci@1" +
              "/pci@700/pci@0/pci@1/pci@0/pci@1/pci@0/pci@1";
        back -> ioaliases;
    };

    Software has developed a script that looks through the alias list, and check for
    device paths below the aliases paths.  Any that exist will be re-written to use the 
    current path. 

       4.1.1 ioalias MD node
	   Name:                  ioalias
	   Category:              optionally required by ioaliases
	   Required Subordinates:
	   Optional Subordinates:
	   Description:           This node provides the current path to a PCIe 
				  switch's upstream port and a list of all possible paths 
				  to the same PCIe switch upstream port.
	   Properties:
   	     Name              Tag        Req'd? Description
             ---------------------------------------------------------------------- 
	     current	   PROP_STR   yes    A string containing the path to a 
					     PCIe switch upstream port.
	     aliases	   PROP_STR   yes    A list of space separated strings containing all the 
					     possible paths to a PCI root nexus.

       4.1.2 ioaliases MD node
	   Name:                  ioaliases
	   Category:              optionally required by root
	   Required Subordinates:
	   Optional Subordinates: ioalias device node
	   Description:           This node provides forward pointers to all 
				  system ioalias nodes

	   For example on Batoka system the ioaliases node would be:
	   node ioaliases ioaliases {
	           fwd -> pcie0;
	           fwd -> pcie1;
	           fwd -> pcie2;
	           fwd -> pcie3;
                   back -> root;
           };


   4.2 Interface tables

    4.2.1 Imported Interfaces

        Name                    Classification  Description
        -----------------       --------------- -------------------
        sun4v Machine           Sun Private     MD nodes definitions as
        Description nodes                       defined by FWARC/2005/115

    4.5.2 Exported Interfaces

        Name                    Classification  Description
        ----------------------  --------------  -------------------
        ioaliases and ioalias    Sun Private     MD nodes defined
        MD nodes                                 by this case