On 9/28/26 4:03 PM, Alexey Charkov wrote:
Hi Quentin,
On Mon, Sep 28, 2026 at 5:26 PM Quentin Schulz <[email protected]> wrote:
Hi Alexey,
On 7/31/26 7:10 PM, Alexey Charkov wrote:
When a generated FIT is used to boot Linux directly, bypassing U-Boot
proper (Falcon mode), there is no runtime code to discover the kernel
command line and (optional) initrd location and include them in a FDT.
To facilitate easier preparation of a ready-to-boot FIT, add support for
pre-patching the FDTs in a FIT with a preconfigured /chosen node including
the bootargs and initrd location.
This sounds wrong to me. Why should we hardcode those at build time? We
already do DT fixups in U-Boot proper *at runtime*, so we should
probably do the same in xPL when booting in Falcon mode instead of
hardcoding stuff. Since you're aware of this, I'm guessing you decided
against, but you don't tell us why. I'm a bit worried going with the
suggested implementation means we'll eventually have a binman node
property for each DT node/property we want to write/override.
The "regular" Falcon way of doing things (i.e. the one not involving
TF-A) has so far been: "capture what U-Boot patches into the args to
be passed to the kernel, package it into a fixed binary, and boot only
that". No runtime fixups. So I more or less followed that pattern, but
tried to make it a bit more accessible by eliminating the "capture
something at runtime and save it somehow somewhere" step, which I find
unnecessarily painful.
Maybe runtime fixups could be brought into xPL, but they are
excruciatingly slow, whereas speed is the main reason for wanting
Falcon mode boot in the first place. Right now with Falcon mode on
RK3576 I'm getting 2.5 seconds from applying power to _userspace_
(i.e. full graphical UI drawn on the screen), whereas the best I could
get with U-Boot is just over 3s to its boot menu, much of that time
spent going over the flat devicetree before relocation in O(n^2)
passes. And those 3s are after stripping the massive pinctrl node with
hundreds of its always-present children from the pre-relocation DT,
which alone saves ~0.4s.
Are they always present, even with /omit-if-no-ref/ instruction? Or
maybe you're building the device trees with -@? Trying to figure out if
somehow we have a bug in dtc (or in our scripts making use of it).
Don't we have FDT and DM in SPL anyway as that's how we probe drivers in
that stage (not counting the few SPL-only boards we have)?
I don't have anything better to suggest, I'm just really worried about
the potential ballooning of properties we need to mirror in binman.
Signed-off-by: Alexey Charkov <[email protected]>
---
tools/binman/entry.py | 8 ++++
tools/binman/etype/fit.py | 103
++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 111 insertions(+)
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index ce7ef28e94b1..e0dea8bf3a49 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -636,6 +636,14 @@ class Entry(object):
self.Detail('GetData: size %s' % to_hex_size(self.data))
return self.data
+ def GetNode(self):
+ """Get the devicetree node which describes this entry
+
+ Returns:
+ Node: Node for this entry
+ """
+ return self._node
+
def GetPaddedData(self, data=None):
"""Get the data for an entry including any padding
diff --git a/tools/binman/etype/fit.py b/tools/binman/etype/fit.py
index 32caa03a7e16..750ff5b47ed5 100644
--- a/tools/binman/etype/fit.py
+++ b/tools/binman/etype/fit.py
@@ -304,6 +304,40 @@ class Entry_fit(Entry_section):
See :ref:`fdtgrep_filter` for more information.
+ Patching /chosen into the generated device trees
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ When the OS is booted directly from this FIT (e.g. Falcon mode) U-Boot
+ proper never runs, so its usual runtime /chosen fixups do not happen. Two
+ optional properties on the `@fdt-SEQ` node make binman patch each generated
+ device tree at build time:
+
+ fit,bootargs
+ A string written to /chosen/bootargs of every generated device tree
+ (any existing value is overwritten). Typically set to `CONFIG_BOOTARGS`
+ via the preprocessed devicetree source.
+
+ fit,initrd
+ The image name of a loadable (e.g. "ramdisk") to use as the initramfs.
+ Its `load` address and packed size are written to
+ /chosen/linux,initrd-start and /chosen/linux,initrd-end (at the width
of
+ the device tree's root #address-cells) and reserved in the FDT
+ memory-reservation map, mirroring fdt_initrd(). If the referenced image
+ is absent or empty (e.g. an optional initramfs that was not supplied)
+ the initrd properties are omitted.
+
This sounds wrong, why would the FDT image node need to know about which
ramdisk may be used? Shouldn't we rather have a ramdisk property in a
configuration node, and then patch the FDT based on that information?
Falcon mode boot where these are useful is for a fixed-configuration
boot flow anyway, where one wouldn't have a way to select among
How do you plan on doing A/B with Falcon boot? How do you know from
which partition the kernel you booted originated so you don't upgrade on
the currently booted partition? There must be some way for U-Boot SPL to
tell the kernel at runtime where it came from?
several ramdisks to go with the kernel image. So putting this
information directly where the user (i.e. the kernel) will find it
cuts out intermediate steps, which in turn improves speed and reduces
complexity.
You already have:
fit,firmware = "atf-1", "kernel", "ramdisk";
fdt = "fdt-SEQ";
in the configuration node. So simply have binman derive from
fit,firmware which node is included of type "ramdisk" and fixup the
device trees in fdt-SEQ based on that info? Less user-prone IMO.
Cheers,
Quentin
