Difference between revisions of "Device tree future"

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(I put linux plumbers 2018 in the wrong place, move it)
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* watch here for session notes
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=== presentation material ===
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* Watch here for slides
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https://etherpad.openstack.org/p/Device_Tree

Revision as of 16:31, 15 November 2018


Top Device Tree page

Devicetree Validation

See section "Devicetree Verification".

Devicetree Verification

references

Presentations about verification.

Linux Plumbers 2015

The verification project made progress around the time of Linux Plumbers 2015, then stalled out.

Linux Plumbers 2016

Grant Likely has re-awakened the project at Linux Plumbers 2016:

Kernel Summit 2017

Grant Likely and Pantelis Antoniou have again re-awakened the project at the Kernel Summit 2017, Devicetree Workshop (and postings to the devicetree mail list shortly before the summit).

Linaro Connect Hong Kong 2018

Grant gave a presentation at Linaro Connect Hong Kong 2018: 

Abstract
Devicetree has become the dominant hardware configuration language used when
building embedded systems. Projects using Devicetree now include Linux, U-Boot,
Android, FreeBSD, and Zephyr. However, it is notoriously difficult to write correct
Devicetree data files. The dtc tools perform limited tests for valid data, and
there is not yet a way to add validity tests for specific hardware descriptions.
Neither is there a good way to document requirements for specific bindings. Work is
underway to solve these problems. This session will present a proposal for adding
Devicetree schema files to the Devicetree toolchain that can be used to both validate
data and produce usable documentation.

Devicetree Specification

Devicetree Specification Release 0.1, located on the Devicetree Specification page has superseded the ePAPR for the Linux kernel.

The Devicetree Specification will continue to be updated.


PDF presentation of the plans for the specification organization and the proposed schedule.

The update process is occurring in the http://webdev.linaro.org/devicetree.org/ devicetree.org organization.

Related discussion occurs on the devicetree-spec email list.

Linux Plumbers 2015 Device Tree Track

presentation material

etherpad notes

https://etherpad.openstack.org/p/LPC2015_Device_Tree

local cache of etherpad notes

final schedule

1:30 Intro
     Frank Rowand
1:35 Device Tree Overlays
     Pantelis Antoniou, Guenter Roeck
2:00 Overlays, some times a good idea sometimes not.
     Pantelis Antoniou
2:15 Device Tree Documentation
     Matt Porter Frank Rowand
2:30 Chat With The dtc Maintainers, part 1
     David Gibson, Jon Loeliger
2:45 ----- Tea Break -----
3:00 Chat With The dtc Maintainers, part 2
     David Gibson, Jon Loeliger
3:10 Overlays and tools for sanity.
     Pantelis Antoniou
3:25 Device Tree Tools
     Frank Rowand
3:40 Device Tree probe order and parallel device probing
     Pantelis Antoniou
3:50 Device tree round up
     Frank Rowand

draft schedule


01 -- Device Tree Overlays - Pantelis
   Device Tree Overlays are now in the mainline kernel. This session
   will cover what they are, how they are used.

   As part of this session I will examine device tree overlays, device
   tree changeset, the phandle resolution mechanism, overlay overlap
   removal checks and finally device tree variants (or quirks).

   Devicetree overlay use in Juniper products - Guenter

   The Juniper use case will be discussed:

   At Juniper, we use devicetree overlays to manage a variety of cards
   which can be inserted and removed at runtime.

   In this session, I will describe the basic system architecture, our
   requirements, and why we decided to use devicetree overlays to meet
   those requirements. I will also dive into the actual implementation
   of our card management framework in the Linux kernel, and explore
   some of the limitations of the current devicetree overlay code.

02 -- was folded into 01

03 -- Overlays, some times a good idea sometimes not. - Pantelis
   This session will cover supported and not supported overlay cases.

04 -- Device Tree Documentation - Frank
   What device tree documentation and tutorials exist and where to find
   them. What is needed?

   What new documentation is expected this year?

   Can we bring consistency to the documentation style/syntax?

05 -- Chat With The dtc Maintainers - Frank
   This session is an opportunity to ask questions of the dtc maintainers
   or listen to their thoughts on dtc related topics.

06 -- Overlays and tools for sanity. - Pantelis
   Device Tree overlays represent a big change for the device tree in
   the kernel. Where as of old the device tree was something static,
   now it's something that can change at runtime.

   We could use some new tools to help us when creating them (compile
   time) and some kernel tooling to help when applying them (run time).

07 -- Device Tree Tools - Frank
   What tools exist to support device tree development and
   debugging? Where are they? What new tools have been proposed or
   requested?

08 -- Device Tree probe order and parallel device probing - Pantelis
   The new dynamic device tree capabilities entails marking not only
   the location of phandles but the references made to them. We can use
   that information to construct a device probe order schedule that can
   be used to support parallel device probing which is an obvious win
   for kernel boot time.

   If earlier sessions run long, this one may be shortened or deleted.

09 -- Device tree round up - Frank
   Review previous sessions, round up loose ends

Material to review before the conference

The purpose of the Linux Plumbers conference is to discuss things. The conference is not a good place to go if you want to look at slides and listen to canned presentations.

The discussions will work better if the attendees have prepared in advance, and have a basic understanding of the technology and issues to be discussed. The goal of this section is to provide the resources needed to be prepared to discuss.

Device Tree 101

If you are new to Device Tree, these resources will start you on the path to a basic understanding.

Overlays

Probe Ordering

Linux Plumbers 2016 Device Tree Track

presentation material

  • [ODP] "Device Tree Schema Discussion"- Grant Likely
  • [PDF] "Device tree Hardware Description vs Configuration vs Policy"- Frank Rowand
  • [PDF] "Device Tree Tools Status" - Frank Rowand

etherpad notes

local cache of etherpad notes

Kernel Summit 2017, Devicetree Workshop

Devicetree Workshop 2017 Group photo

There was a Devicetree Workshop held as part of the Linux Kernel Summit on 26 October 2017 in Prague. Some photos of the event can be found in the OSSummit Europe / ELCE photostream on Flickr.

Presentation Materials

  • [PDF] Agenda slides
  • [JPG] Devicetree data flow drawing - Frank Rowand
  • [PDF] "YAML and Devicetree" web blog - Pantelis Antoniou
  • [YAML] [JSON] Sample DT encoded YAML and matching jsonschema - Grant Likely.
  • [PDF] "Devicetree in Zephyr" - Kumar Gala
  • [PDF] "Device tree in U-Boot SPL" - Simon Glass
  • [PDF] "DT Generic Bindings" - Geert Uytterhoeven
  • [PDF] "Duplicate Data" - Thomas Petazzoni
  • [PDF] "Foreign Bindings" - Maxime Ripard

Example validator code for jsonschema

This is the sample validator code block shown for the jsonschema materials above 

#!/usr/bin/env python3
import sys
import yaml
import jsonschema
schema = yaml.load(open("dt-schema-core.json").read())
testtree = yaml.load(open("juno.cpp.yaml").read())
v = jsonschema.Draft4Validator(schema)
errors = sorted(v.iter_errors(testtree), key=lambda e: e.path)
for error in errors:
    print(error.path, error.message)

Notes

Audio Recording

Grant Likely has audio recordings of the entire workshop, but they are large files and haven't been published yet. Contact Grant if you want a copy of the audio.

Action Items

Linux Plumbers 2018

presentation material

  • Watch here for slides

etherpad notes

https://etherpad.openstack.org/p/Device_Tree

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