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cmd: pxe: add alias devicetree-overlay for fdtoverlays

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This adds keyword devicetree-overlay as an alias for fdtoverlays in
extlinux (sysboot) and pxe to better follow the Boot Loader Specification
[1], improves documentation around them by adding an example for both
fdtoverlays and devicetree-overlay and the environment variable required
for this feature. The link for the spec is updated to the current one.

[1] https://systemd.io/BOOT_LOADER_SPECIFICATION/

Signed-off-by: Edoardo Tomelleri <e.tomell@gmail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
This commit is contained in:
Edoardo Tomelleri 2022-09-21 15:26:33 +02:00 committed by Tom Rini
parent 300077cf8c
commit 35821a25c1
3 changed files with 43 additions and 3 deletions
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2
boot/pxe_utils.c
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@ -380,6 +380,7 @@ err:
/**
* label_boot_fdtoverlay() - Loads fdt overlays specified in 'fdtoverlays'
* or 'devicetree-overlay'
*
* @ctx: PXE context
* @label: Label to process
@ -809,6 +810,7 @@ static const struct token keywords[] = {
{"devicetreedir", T_FDTDIR},
{"fdtdir", T_FDTDIR},
{"fdtoverlays", T_FDTOVERLAYS},
{"devicetree-overlay", T_FDTOVERLAYS},
{"ontimeout", T_ONTIMEOUT,},
{"ipappend", T_IPAPPEND,},
{"background", T_BACKGROUND,},

12
doc/README.pxe
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@ -163,6 +163,13 @@ fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
and then applied in the load order to the fdt blob stored at the
address indicated in the fdt_addr_r environment variable.
devicetree-overlay <path> [...] - if this label is chosen, use tftp to retrieve the DT
overlay(s) at <path>. it will be temporarily stored at the
address indicated in the fdtoverlay_addr_r environment variable,
and then applied in the load order to the fdt blob stored at the
address indicated in the fdt_addr_r environment variable.
Alias for fdtoverlays.
kaslrseed - set this label to request random number from hwrng as kaslr seed.
append <string> - use <string> as the kernel command line when booting this
@ -178,6 +185,11 @@ fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
the fdt_addr_r environment variable, and that address will
be passed to bootm.
devicetree <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. Alias for fdt.
fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob
relative to <path>. If the fdtfile environment variable
is set, <path>/<fdtfile> is retrieved. Otherwise, the

32
doc/develop/distro.rst
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@ -68,10 +68,10 @@ Boot Configuration Files
The standard format for boot configuration files is that of extlinux.conf, as
handled by U-Boot's "syslinux" (disk) or "pxe boot" (network). This is roughly
as specified at BootLoaderSpec_:
as specified at `Boot Loader Specification`_:
... with the exceptions that the BootLoaderSpec document:
... with the exceptions that the Boot Loader Specification document:
* Prescribes a separate configuration per boot menu option, whereas U-Boot
lumps all options into a single extlinux.conf file. Hence, U-Boot searches
@ -81,6 +81,8 @@ as specified at BootLoaderSpec_:
* Does not document the fdtdir option, which automatically selects the DTB to
pass to the kernel.
See also doc/README.pxe under 'pxe file format'.
One example extlinux.conf generated by the Fedora installer is::
# extlinux.conf generated by anaconda
@ -115,6 +117,25 @@ One example extlinux.conf generated by the Fedora installer is::
fdtdir /boot/dtb-3.16.0-0.rc6.git1.1.fc22.armv7hl+lpae
One example of hand-crafted extlinux.conf::
menu title Select kernel
timeout 100
label Arch with uart devicetree overlay
kernel /arch/Image.gz
initrd /arch/initramfs-linux.img
fdt /dtbs/arch/board.dtb
fdtoverlays /dtbs/arch/overlay/uart0-gpio0-1.dtbo
append console=ttyS0,115200 console=tty1 rw root=UUID=fc0d0284-ca84-4194-bf8a-4b9da8d66908
label Arch with uart devicetree overlay but with Boot Loader Specification keys
kernel /arch/Image.gz
initrd /arch/initramfs-linux.img
devicetree /dtbs/arch/board.dtb
devicetree-overlay /dtbs/arch/overlay/uart0-gpio0-1.dtbo
append console=ttyS0,115200 console=tty1 rw root=UUID=fc0d0284-ca84-4194-bf8a-4b9da8d66908
Another hand-crafted network boot configuration file is::
TIMEOUT 100
@ -214,6 +235,11 @@ fdt_addr_r:
A size of 1MB for the FDT/DTB seems reasonable.
fdtoverlay_addr_r:
Mandatory. The location in RAM where DTB overlays will be temporarily
stored and then applied in the load order to the fdt blob stored at the
address indicated in the fdt_addr_r environment variable.
fdtfile:
Mandatory. the name of the DTB file for the specific board for instance
the espressobin v5 board the value is "marvell/armada-3720-espressobin.dtb"
@ -408,7 +434,7 @@ way in future u-boot versions. In particular the <device type>_boot
variables (e.g. mmc_boot, usb_boot) are a strictly internal implementation
detail and must not be used as a public interface.
.. _BootLoaderSpec: http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/
.. _`Boot Loader Specification`: https://systemd.io/BOOT_LOADER_SPECIFICATION/
.. sectionauthor:: (C) Copyright 2014 Red Hat Inc.
.. sectionauthor:: Copyright (c) 2014-2015, NVIDIA CORPORATION. All rights reserved.