/*
   * Copyright 2010-2011 Calxeda, Inc.
   *

   * SPDX-License-Identifier:	GPL-2.0+

   */
  
  The 'pxe' commands provide a near subset of the functionality provided by
  the PXELINUX boot loader. This allows U-boot based systems to be controlled
  remotely using the same PXE based techniques that many non U-boot based servers
  use.
  
  Commands
  ========
  
  pxe get
  -------
       syntax: pxe get
  
       follows PXELINUX's rules for retrieving configuration files from a tftp
       server, and supports a subset of PXELINUX's config file syntax.
  
       Environment
       -----------
       'pxe get' requires two environment variables to be set:
  
       pxefile_addr_r - should be set to a location in RAM large enough to hold
       pxe files while they're being processed. Up to 16 config files may be
       held in memory at once. The exact number and size of the files varies with
       how the system is being used. A typical config file is a few hundred bytes
       long.
  
       bootfile,serverip - these two are typically set in the DHCP response
       handler, and correspond to fields in the DHCP response.
  
       'pxe get' optionally supports these two environment variables being set:
  
       ethaddr - this is the standard MAC address for the ethernet adapter in use.
       'pxe get' uses it to look for a configuration file specific to a system's
       MAC address.
  
       pxeuuid - this is a UUID in standard form using lower case hexadecimal
       digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
       it to look for a configuration file based on the system's UUID.
  
       File Paths
       ----------
       'pxe get' repeatedly tries to download config files until it either
       successfully downloads one or runs out of paths to try. The order and
       contents of paths it tries mirrors exactly that of PXELINUX - you can
       read in more detail about it at:
  
       http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
  
  pxe boot
  --------
       syntax: pxe boot [pxefile_addr_r]
  
       Interprets a pxe file stored in memory.
  
       pxefile_addr_r is an optional argument giving the location of the pxe file.
       The file must be terminated with a NUL byte.
  
       Environment
       -----------
       There are some environment variables that may need to be set, depending
       on conditions.
  
       pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
       an environment variable named pxefile_addr_r must be supplied. This is
       typically the same value as is used for the 'pxe get' command.
  
       bootfile - typically set in the DHCP response handler based on the
       same field in the DHCP respone, this path is used to generate the base
       directory that all other paths to files retrieved by 'pxe boot' will use.
       If no bootfile is specified, paths used in pxe files will be used as is.
  
       serverip - typically set in the DHCP response handler, this is the IP
       address of the tftp server from which other files will be retrieved.
  
       kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
       store the kernel and initrd it retrieves from tftp. These locations will
       be passed to the bootm command to boot the kernel. These environment
       variables are required to be set.

       fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
       retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
       pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
       will be passed to bootm command to boot the kernel.
  
       fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
       command if it is set and 'fdt_addr_r' is not passed to bootm command.

  
  pxe file format
  ===============
  The pxe file format is nearly a subset of the PXELINUX file format; see
  http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
  commands - global commands, and commands specific to labels. Lines begining
  with # are treated as comments. White space between and at the beginning of
  lines is ignored.
  
  The size of pxe files and the number of labels is only limited by the amount
  of RAM available to U-boot. Memory for labels is dynamically allocated as
  they're parsed, and memory for pxe files is statically allocated, and its
  location is given by the pxefile_addr_r environment variable. The pxe code is
  not aware of the size of the pxefile memory and will outgrow it if pxe files
  are too large.
  
  Supported global commands
  -------------------------
  Unrecognized commands are ignored.

  default <label>	    - the label named here is treated as the default and is
  		      the first label 'pxe boot' attempts to boot.

  
  menu title <string> - sets a title for the menu of labels being displayed.
  
  menu include <path> - use tftp to retrieve the pxe file at <path>, which

  		      is then immediately parsed as if the start of its
  		      contents were the next line in the current file. nesting
  		      of include up to 16 files deep is supported.

  prompt <flag>	    - if 1, always prompt the user to enter a label to boot
  		      from. if 0, only prompt the user if timeout expires.

  
  timeout <num>	    - wait for user input for <num>/10 seconds before

  		      auto-booting a node.

  label <name>	    - begin a label definition. labels continue until
  		      a command not recognized as a label command is seen,
  		      or EOF is reached.

  
  Supported label commands
  ------------------------
  labels end when a command not recognized as a label command is reached, or EOF.

  menu default	    - set this label as the default label to boot; this is
  		      the same behavior as the global default command but
  		      specified in a different way

  kernel <path>	    - if this label is chosen, use tftp to retrieve the kernel
  		      at <path>. it will be stored at the address indicated in
  		      the kernel_addr_r environment variable, and that address
  		      will be passed to bootm to boot this kernel.

  append <string>	    - use <string> as the kernel command line when booting this
  		      label.

  initrd <path>	    - if this label is chosen, use tftp to retrieve the initrd
  		      at <path>. it will be stored at the address indicated in
  		      the initrd_addr_r environment variable, and that address
  		      will be passed to bootm.

  fdt <path>	    - if this label is chosen, use tftp to retrieve the fdt blob
  		      at <path>. it will be stored at the address indicated in
  		      the fdt_addr_r environment variable, and that address will
  		      be passed to bootm.

  localboot <flag>    - Run the command defined by "localcmd" in the environment.

  		      <flag> is ignored and is only here to match the syntax of
  		      PXELINUX config files.

  
  Example
  -------
  Here's a couple of example files to show how this works.
  
  ------------/tftpboot/pxelinux.cfg/menus/linux.list----------
  menu title Linux selections
  
  # This is the default label
  label install
  	menu label Default Install Image
  	kernel kernels/install.bin
  	append console=ttyAMA0,38400 debug earlyprintk
  	initrd initrds/uzInitrdDebInstall
  
  # Just another label
  label linux-2.6.38
  	kernel kernels/linux-2.6.38.bin
  	append root=/dev/sdb1
  
  # The locally installed kernel
  label local
  	menu label Locally installed kernel
  	append root=/dev/sdb1
  	localboot 1
  -------------------------------------------------------------
  
  ------------/tftpboot/pxelinux.cfg/default-------------------
  menu include pxelinux.cfg/menus/base.menu
  timeout 500
  
  default linux-2.6.38
  -------------------------------------------------------------
  
  When a pxe client retrieves and boots the default pxe file,
  'pxe boot' will wait for user input for 5 seconds before booting
  the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
  to be downloaded, and boot with the command line "root=/dev/sdb1"
  
  Differences with PXELINUX
  =========================
  The biggest difference between U-boot's pxe and PXELINUX is that since
  U-boot's pxe support is written entirely in C, it can run on any platform
  with network support in U-boot. Here are some other differences between
  PXELINUX and U-boot's pxe support.
  
  - U-boot's pxe does not support the PXELINUX DHCP option codes specified
    in RFC 5071, but could be extended to do so.
  
  - when U-boot's pxe fails to boot, it will return control to U-boot,
    allowing another command to run, other U-boot command, instead of resetting
    the machine like PXELINUX.
  
  - U-boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
    only uses U-boot.
  
  - U-boot's pxe doesn't provide the full menu implementation that PXELINUX
    does, only a simple text based menu using the commands described in

    this README.	With PXELINUX, it's possible to have a graphical boot

    menu, submenus, passwords, etc. U-boot's pxe could be extended to support
    a more robust menuing system like that of PXELINUX's.
  
  - U-boot's pxe expects U-boot uimg's as kernels.  Anything that would work
    with the 'bootm' command in U-boot could work with the 'pxe boot' command.

  - U-boot's pxe only recognizes a single file on the initrd command line.  It
    could be extended to support multiple.
  
  - in U-boot's pxe, the localboot command doesn't necessarily cause a local
    disk boot - it will do whatever is defined in the 'localcmd' env
    variable. And since it doesn't support a full UNDI/PXE stack, the
    type field is ignored.
  
  - the interactive prompt in U-boot's pxe only allows you to choose a label
    from the menu.  If you want to boot something not listed, you can ctrl+c
    out of 'pxe boot' and use existing U-boot commands to accomplish it.