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Fwd: [devicetree-org/dt-schema] schemas: chosen: document devicetree-path property (PR #167)

by Rob Herring

Posting to boot-architecture list for more visibility. ---------- Forwarded message --------- From: Casey Connolly <notifications(a)github.com> Date: Mon, Jun 30, 2025 at 12:33 PM Subject: [devicetree-org/dt-schema] schemas: chosen: document devicetree-path property (PR #167) To: devicetree-org/dt-schema <dt-schema(a)noreply.github.com> Cc: Subscribed <subscribed(a)noreply.github.com> Background With more and more laptops, dev boards, and other products shipping with both an EFI capable bootloader and relying on devicetree, there is an increasing problem with trying to ensure that a devicetree is loaded and that it will work with the kernel/OS version being booted. This is less of an issue on vertically integrated embedded platforms, but with ARM SystemReady gaining prevalence and the abundance of cheap dev boards there is a growing desire to boot generic OS installer/disk images on these devices. In some cases the platform doesn't see many devicetree changes and works well with a range of kernel versions, the board can just provide it's own devicetree in firmware and it will work just fine. However there are many platforms where this is not the case, unintentional breaking changes can be made to drivers or DT, or new features being enabled can break compatibility with older kernels. In these cases, the best way to maximise the chance that the generic OS image will boot is if it can load the devicetree blob which was installed alongside the kernel (something most mainstream distros do). To enable this there has to be a consistent way to determine which dtb (and overlays) were embedded into the firmware provided devicetree. This new property enables exactly this usecase by making it possible to embed the information into the dtb itself at build time. A proposed implementation of this for U-Boot is available here 1. The devicetree paths are all appended to some versioned prefix (typically the kernel version) which would be known by the OS loader when you choose a version to boot. Prior effort Previous attempts have been made to work around the issue of DTB loading, U-Boot attempts to search some well-known (unversioned) paths on the ESP using it's internal fdtfile variable (which has to be constructed in a platform specific way, see below). This has mixed results and doesn't work on distros like Fedora and Debian which install dtbs to version-specific subdirectories. On the EFI laptop side (where they don't provide any DTB) the dtbloader EFI driver effectively implements the same logic as U-Boot, guessing generic paths and using an internal unreliable map of SMBIOS hardware IDs to file paths, this has been the go-to for many folks for a while now but it's clear that it doesn't scale and that distros won't be keep to ship it. It gets more complicated when you consider secureboot as well which would require signing the driver. File path as API This proposed solution does have a potential stumbling block, as it effectively cements the idea that the dtb path is API. I believe this is a bridge that was already crossed long ago when extlinux and later GRUB and systemd-boot gained a way to specify a devicetree blob to load, since all distros use the upstream file naming, any renames already potentially cause devices to become unbootable after a kernel upgrade... That being said, it's clear that the current way files are named is often arbitrary and definitely inconsistent. I would propose a solution like enforcing a way to convert between the root compatible property and the file path, this provides consistency and removes the need to store this arbitrary additional data needed to locate the dtb on the ESP during boot. An ugly attempt to best-effort this conversion for Qualcomm boards today can be found at 2. Why not store this data elsewhere? There are quite a few benefits to putting this in the DTB itself. It makes it possible to have a generic bootloader binary which gets the DTB in an implementation-specific way, it avoids having to hard-code the data. On devices that have an EFI which doesn't provide a DTB, a driver can be installed once on the ESP which installs a stub DT just containing these properties, so that the OS loader can use them. It isn't EFI specific, extlinux or other boot methods can make use of this. This is metadata which belongs with the DTB, it can be inserted at build time or at runtime, or even augmented to add additional overlays at runtime should the implementation require that. All in all, a generic mechanism for bootloaders and OS loaders to load a dtb and overlays from the ESP (or other arbitrary storage mechanism) is needed, and there doesn't seem to be another place to put it. Why not FIT? The FIT format has it's uses in embedded applications, but the only way it could be applied here would be to use it as the way to index /all/ of the available DTBs, in a generic ARM64 Fedora or Debian image there are thousands of these. In addition, while matching by compatible property may work for the base DTB, it doesn't work for overlays. And of course, using FIT for this would require changing how DTBs are installed and packaged, this would be hugely disruptive and introduce a myriad of additional problems. cc @poettering @apalos ________________________________ You can view, comment on, or merge this pull request online at: https://github.com/devicetree-org/dt-schema/pull/167 Commit Summary bb9677f schemas: chosen: document devicetree-path property File Changes (1 file) M dtschema/schemas/chosen.yaml (22) Patch Links: https://github.com/devicetree-org/dt-schema/pull/167.patch https://github.com/devicetree-org/dt-schema/pull/167.diff — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.Message ID: <devicetree-org/dt-schema/pull/167(a)github.com>

1 year

Call for Participation: Embedded & IoT micro-conference at Linux Plumbers 2025

by Jan Lübbe

We are happy to announce that the Embedded & IoT micro-conference was again accepted for Linux Plumbers this year. Hosted in beautiful Tokyo, Japan December 11-13. https://lpc.events/event/19/contributions/2005/ Topics cover all things embedded and IoT. Boot time to kernel size, low power communication, telemetry and also RTOS. Devicetree and build system have their own MC and we can move sessions between them as needed. As with all MC's at Plumbers we are not looking for talks, but rather discussing current problems and working towards their solution. If your proposal has a specific stakeholder (maintainer, developer, company) that would be needed for a fruitful discussion, please mention it in your submission. The CfP is open now and will run until October 3rd. Please do not wait until the end with your submissions as we are going to accept good proposals even before the end, so the MC might be filled up before October 3rd. Jan & Stefan

1 year

EBBR call today Aug 27

by Vincent Stehlé

Dear EBBR contributors, I hope you had a nice summer break. We will have our EBBR call today, Aug 27 at 14:00 BST (13:00 UTC). [1] We have a few topics on the agenda [2]: - First look at pull request #144: PFDI requirements - Pull request #145: Harmonize sections references titles - Pull request #146: Bump references We will not "vote" on the PFDI requirements on this call, as I suspect not everybody might be back yet, but for the next two minor pull requests we might. We can use this pad [3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-aug-27-agfi?lang=en #144: https://github.com/ARM-software/ebbr/pull/144 #145: https://github.com/ARM-software/ebbr/pull/145 #146: https://github.com/ARM-software/ebbr/pull/146

1 year

u-boot question regarding the rockchip rk 3399...

by Mario Marietto

Hello. I've installed FreeBSD 14.2-RELEASE on both my boards (RockPro64 and Khadas Edge V),both based on the Rockchip RK3399 and I've used a display that has a resolution of 720 x 720 resolution and I saw that the screen remains almost black (almost because I see a dim illumination coming from the display) . I don't even see the u-boot logo. Instead,it is able to turn on my large HDMI monitor,which has a resolution of 1920x1080 pixels. Since I'm building a FreeBSD modular phone, I want to use a small HDMI display with a low resolution. My question is : why is u-boot able to turn on a monitor that has a resolution of 1920x1080 and it's not able to turn on the other HDMI display that has a resolution of 720x720 ? Or even better : what's the lowest resolution that will work ? If I want to buy a display that has a resolution of 800x600,will u-boot be able to turn it on ? 1024x768 ? more ? Thanks. -- Mario.

1 year

Next EBBR call Aug 27

by Vincent Stehlé

Hi, This is a quick reminder that we will not have an EBBR call today and the next one will be on Aug 27. [1] Best regards, Vincent Stehlé System Architect - Arm [1] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings

1 year, 2 months

EBBR call today Jun 18

by Vincent Stehlé

Dear EBBR contributors, We will have an EBBR call today, Jun 18 at 14:00 BST (13:00 UTC). [1] We have mostly only one topic on the agenda [2], therefore this could be a short call: - Summary of the investigations for pull request #141 ("All runtime services optional after ExitBootServices()") - Let's decide if we drop it completely. Otherwise if people are motivated enough we could always cleanup old issues and pull requests. We can use this pad[3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-jun-18-af4v?lang=en #141 https://github.com/ARM-software/ebbr/pull/141

1 year, 2 months

No EBBR call today Jun 4?

by Vincent Stehlé

Hi, We have no agenda for today's EBBR call [1], therefore I suspect we might end up canceling it. If you have an urgent topic to discuss today, please let us know before 11am UTC, otherwise we will adjourn the call. Best regards, Vincent Stehlé System Architect - Arm [1] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings

1 year, 3 months

No EBBR call today May 21?

by Vincent Stehlé

Hi, We have no agenda for today's EBBR call [1], therefore I wonder if we might as well cancel it. If you have an urgent topic to discuss today, please let us know before 11am UTC, otherwise we will adjourn the call. Best regards, Vincent Stehlé System Architect - Arm [1] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings

1 year, 3 months

EBBR call today May 7

by Vincent Stehlé

Dear EBBR contributors, We will have an EBBR call today, May 7 at 14:00 BST (13:00 UTC). [1] We have only one topic on the agenda [2], therefore this could be a short call: - Pull request #142: Conditionally require SCMI 2.x, x >= 1 recommended We can use this pad[3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-may-7-aecv?lang=en #142 https://github.com/ARM-software/ebbr/pull/142

1 year, 4 months

EBBR call today Apr 23

by Vincent Stehlé

Dear EBBR contributors, We will have an EBBR call today, Apr 23 at 14:00 BST (13:00 UTC). [1] On the agenda: [2] - Pull request #141: All runtime services optional after ExitBootServices(). - Pull request #142: Conditionally require SCMI 2.x, x >= 1 recommended We can use this pad[3] for the meeting notes. Feel free to add to the agenda, directly on the wiki page, by e-mail or on the pad. Best regards, Vincent Stehlé System Architect - Arm [1] https://armltd.zoom.us/j/92081365511?pwd=SFZpRitXUEp3Zy9GM0h3UUZ1b1pnUT09 [2] https://github.com/ARM-software/ebbr/wiki/EBBR-Meetings [3] https://mensuel.framapad.org/p/ebbr-call-of-23-apr-ae3j?lang=en #141 https://github.com/ARM-software/ebbr/pull/141 #142 https://github.com/ARM-software/ebbr/pull/142

1 year, 4 months

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