1SPDX-License-Identifier: GPL-2.0+
2/*
3 * Copyright 2010-2011 Calxeda, Inc.
4 */
5
6The 'pxe' commands provide a near subset of the functionality provided by
7the PXELINUX boot loader. This allows U-Boot based systems to be controlled
8remotely using the same PXE based techniques that many non U-Boot based servers
9use.
10
11Commands
12========
13
14pxe get
15-------
16     syntax: pxe get
17
18     follows PXELINUX's rules for retrieving configuration files from a tftp
19     server, and supports a subset of PXELINUX's config file syntax.
20
21     Environment
22     -----------
23     'pxe get' requires two environment variables to be set:
24
25     pxefile_addr_r - should be set to a location in RAM large enough to hold
26     pxe files while they're being processed. Up to 16 config files may be
27     held in memory at once. The exact number and size of the files varies with
28     how the system is being used. A typical config file is a few hundred bytes
29     long.
30
31     bootfile,serverip - these two are typically set in the DHCP response
32     handler, and correspond to fields in the DHCP response.
33
34     'pxe get' optionally supports these two environment variables being set:
35
36     ethaddr - this is the standard MAC address for the ethernet adapter in use.
37     'pxe get' uses it to look for a configuration file specific to a system's
38     MAC address.
39
40     pxeuuid - this is a UUID in standard form using lower case hexadecimal
41     digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
42     it to look for a configuration file based on the system's UUID.
43
44     File Paths
45     ----------
46     'pxe get' repeatedly tries to download config files until it either
47     successfully downloads one or runs out of paths to try. The order and
48     contents of paths it tries mirrors exactly that of PXELINUX - you can
49     read in more detail about it at:
50
51     http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
52
53pxe boot
54--------
55     syntax: pxe boot [pxefile_addr_r]
56
57     Interprets a pxe file stored in memory.
58
59     pxefile_addr_r is an optional argument giving the location of the pxe file.
60     The file must be terminated with a NUL byte.
61
62     Environment
63     -----------
64     There are some environment variables that may need to be set, depending
65     on conditions.
66
67     pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
68     an environment variable named pxefile_addr_r must be supplied. This is
69     typically the same value as is used for the 'pxe get' command.
70
71     bootfile - typically set in the DHCP response handler based on the
72     same field in the DHCP respone, this path is used to generate the base
73     directory that all other paths to files retrieved by 'pxe boot' will use.
74     If no bootfile is specified, paths used in pxe files will be used as is.
75
76     serverip - typically set in the DHCP response handler, this is the IP
77     address of the tftp server from which other files will be retrieved.
78
79     kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
80     store the kernel(or FIT image) and initrd it retrieves from tftp. These
81     locations will be passed to the bootm command to boot the kernel. These
82     environment variables are required to be set.
83
84     fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
85     retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
86     pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
87     will be passed to bootm command to boot the kernel.
88
89     fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
90     command if it is set and 'fdt_addr_r' is not passed to bootm command.
91
92     fdtoverlay_addr_r - location in RAM at which 'pxe boot' will temporarily store
93     fdt overlay(s) before applying them to the fdt blob stored at 'fdt_addr_r'.
94
95     pxe_label_override - override label to be used, if exists, instead of the
96     default label. This will allow consumers to choose a pxe label at
97     runtime instead of having to prompt the user. If "pxe_label_override" is set
98     but does not exist in the pxe menu, pxe would fallback to the default label if
99     given, and no failure is returned but rather a warning message.
100
101pxe file format
102===============
103The pxe file format is nearly a subset of the PXELINUX file format; see
104http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
105commands - global commands, and commands specific to labels. Lines begining
106with # are treated as comments. White space between and at the beginning of
107lines is ignored.
108
109The size of pxe files and the number of labels is only limited by the amount
110of RAM available to U-Boot. Memory for labels is dynamically allocated as
111they're parsed, and memory for pxe files is statically allocated, and its
112location is given by the pxefile_addr_r environment variable. The pxe code is
113not aware of the size of the pxefile memory and will outgrow it if pxe files
114are too large.
115
116Supported global commands
117-------------------------
118Unrecognized commands are ignored.
119
120default <label>	    - the label named here is treated as the default and is
121		      the first label 'pxe boot' attempts to boot.
122
123menu title <string> - sets a title for the menu of labels being displayed.
124
125menu include <path> - use tftp to retrieve the pxe file at <path>, which
126		      is then immediately parsed as if the start of its
127		      contents were the next line in the current file. nesting
128		      of include up to 16 files deep is supported.
129
130prompt <flag>	    - if 1, always prompt the user to enter a label to boot
131		      from. if 0, only prompt the user if timeout expires.
132
133timeout <num>	    - wait for user input for <num>/10 seconds before
134		      auto-booting a node.
135
136label <name>	    - begin a label definition. labels continue until
137		      a command not recognized as a label command is seen,
138		      or EOF is reached.
139
140Supported label commands
141------------------------
142labels end when a command not recognized as a label command is reached, or EOF.
143
144menu default	    - set this label as the default label to boot; this is
145		      the same behavior as the global default command but
146		      specified in a different way
147
148kernel <path>	    - if this label is chosen, use tftp to retrieve the kernel
149		      (or FIT image) at <path>. it will be stored at the address
150		      indicated in the kernel_addr_r environment variable, and
151		      that address will be passed to bootm to boot this kernel.
152		      For FIT image, The configuration specification can be
153		      appended to the file name, with the format:
154		        <path>#<conf>[#<extra-conf[#...]]
155		      It will passed to bootm with that address.
156		      (see: doc/uImage.FIT/command_syntax_extensions.txt)
157		      It useful for overlay selection in pxe file
158		      (see: doc/uImage.FIT/overlay-fdt-boot.txt)
159
160fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
161                      overlay(s) at <path>. it will be temporarily stored at the
162                      address indicated in the fdtoverlay_addr_r environment variable,
163                      and then applied in the load order to the fdt blob stored at the
164                      address indicated in the fdt_addr_r environment variable.
165
166devicetree-overlay <path> [...] - if this label is chosen, use tftp to retrieve the DT
167                      overlay(s) at <path>. it will be temporarily stored at the
168                      address indicated in the fdtoverlay_addr_r environment variable,
169                      and then applied in the load order to the fdt blob stored at the
170                      address indicated in the fdt_addr_r environment variable.
171                      Alias for fdtoverlays.
172
173kaslrseed           - set this label to request random number from hwrng as kaslr seed.
174
175append <string>	    - use <string> as the kernel command line when booting this
176		      label.
177
178initrd <path>	    - if this label is chosen, use tftp to retrieve the initrd
179		      at <path>. it will be stored at the address indicated in
180		      the initrd_addr_r environment variable, and that address
181		      will be passed to bootm.
182		      For FIT image, the initrd can be provided with the same value than
183		      kernel, including configuration:
184		        <path>#<conf>[#<extra-conf[#...]]
185		      In this case, kernel_addr_r is passed to bootm.
186
187fdt <path>	    - if this label is chosen, use tftp to retrieve the fdt blob
188		      at <path>. it will be stored at the address indicated in
189		      the fdt_addr_r environment variable, and that address will
190		      be passed to bootm.
191		      For FIT image, the device tree can be provided with the same value
192		      than kernel, including configuration:
193		        <path>#<conf>[#<extra-conf[#...]]
194		      In this case, kernel_addr_r is passed to bootm.
195
196devicetree <path>   - if this label is chosen, use tftp to retrieve the fdt blob
197		      at <path>. it will be stored at the address indicated in
198		      the fdt_addr_r environment variable, and that address will
199		      be passed to bootm. Alias for fdt.
200
201fdtdir <path>	    - if this label is chosen, use tftp to retrieve a fdt blob
202		      relative to <path>. If the fdtfile environment variable
203		      is set, <path>/<fdtfile> is retrieved. Otherwise, the
204		      filename is generated from the soc and board environment
205		      variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
206		      If the fdt command is specified, fdtdir is ignored.
207
208localboot <flag>    - Run the command defined by "localcmd" in the environment.
209		      <flag> is ignored and is only here to match the syntax of
210		      PXELINUX config files.
211
212Example
213-------
214Here's a couple of example files to show how this works.
215
216------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
217menu title Linux selections
218
219# This is the default label
220label install
221	menu label Default Install Image
222	kernel kernels/install.bin
223	append console=ttyAMA0,38400 debug earlyprintk
224	initrd initrds/uzInitrdDebInstall
225
226# Just another label
227label linux-2.6.38
228	kernel kernels/linux-2.6.38.bin
229	append root=/dev/sdb1
230
231# The locally installed kernel
232label local
233	menu label Locally installed kernel
234	append root=/dev/sdb1
235	localboot 1
236-------------------------------------------------------------
237
238------------/tftpboot/pxelinux.cfg/default-------------------
239menu include pxelinux.cfg/menus/base.menu
240timeout 500
241
242default linux-2.6.38
243-------------------------------------------------------------
244
245When a pxe client retrieves and boots the default pxe file,
246'pxe boot' will wait for user input for 5 seconds before booting
247the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
248to be downloaded, and boot with the command line "root=/dev/sdb1"
249
250Differences with PXELINUX
251=========================
252The biggest difference between U-Boot's pxe and PXELINUX is that since
253U-Boot's pxe support is written entirely in C, it can run on any platform
254with network support in U-Boot. Here are some other differences between
255PXELINUX and U-Boot's pxe support.
256
257- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
258  in RFC 5071, but could be extended to do so.
259
260- when U-Boot's pxe fails to boot, it will return control to U-Boot,
261  allowing another command to run, other U-Boot command, instead of resetting
262  the machine like PXELINUX.
263
264- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
265  only uses U-Boot.
266
267- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
268  does, only a simple text based menu using the commands described in
269  this README.	With PXELINUX, it's possible to have a graphical boot
270  menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
271  a more robust menuing system like that of PXELINUX's.
272
273- U-Boot's pxe expects U-Boot uimg's as kernels.  Anything that would work
274  with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
275
276- U-Boot's pxe only recognizes a single file on the initrd command line.  It
277  could be extended to support multiple.
278
279- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
280  disk boot - it will do whatever is defined in the 'localcmd' env
281  variable. And since it doesn't support a full UNDI/PXE stack, the
282  type field is ignored.
283
284- the interactive prompt in U-Boot's pxe only allows you to choose a label
285  from the menu.  If you want to boot something not listed, you can ctrl+c
286  out of 'pxe boot' and use existing U-Boot commands to accomplish it.
287