From: eLinux.org

Device tree future

Contents

• 1 Where Device Tree is Headed
  • 1.1 Resources for the Linux Plumbers 2015 Device Tree
    Track
    • 1.1.1 Material to review before the
      event
      • 1.1.1.1 Device Tree 101
      • 1.1.1.2 Overlays
      • 1.1.1.3 documentation
      • 1.1.1.4 dtc
      • 1.1.1.5 Probe Ordering
      • 1.1.1.6 device tree debugging
        tools
    • 1.1.2 Current draft of the
      schedule

Where Device Tree is Headed

Resources for the Linux Plumbers 2015 Device Tree Track

THIS SECTION IS UNDER CONSTRUCTION

Material to review before the event

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.

• An introduction
  • Device trees I: Are we having fun
    yet? - Neil Brown, LWN.net
    November 2013
  • Device trees II: The harder
    parts - Neil Brown, LWN.net
    November 2013
  • “Device Tree for Dummies”, ELC 2014 by Thomas Petazzoni
    • PDF
    • YouTube video
• More advanced material
  • “The Device Tree as a Stable ABI: A Fairy Tale?”, ELC 2015 by
    Thomas Petazzoni
    • http://elinux.org/images/0/0a/The_Device_Tree_as_a_Stable_ABI-_A_Fairy_Tale%3F.pdf
  • “Device Tree, the Disaster so Far”, ELC Europe 2013 by Mark
    Rutland
    • Media:Rutland-presentation_3.pdf
    • YouTube video

Overlays

• “Transactional Device Tree & Overlays: Making Reconfigurable
  Hardware Work”, ELC 2015 by Pantelis Antoniou
  • PDF
  • YouTube video
• Problem statements
  • IO boards, eg beaglebone capes
  • PPC sub-tree beneath hot-plug PCI
    • http://www.spinics.net/lists/linux-pci/msg40740.html
    • It might be possible to use existing dynamic add and remove
      functions (CONFIG_OF_DYNAMIC) for this purpose
  • Quirks - TODO
    • [PATCH
      0/4
      Device Tree Quirks & the Beaglebone]
    • cpu card plugged into multiple carrier card variants, post
      manufacturing
  • devices present only during manufacturing
    • Dealing with optional i2c devices in a
      devicetree

documentation

dtc

Probe Ordering

• Tomeu Vizoso
  • First approach: [PATCH
    00/21
    On-demand device registration]
  • Second approach: [PATCH
    00/13
    Discover and probe dependencies]
• Other….

device tree debugging tools

Current draft of the schedule

Expect this to evolve.

01 -- Device Tree Overlays - Pantelis
      Devicetree overlay use in Juniper products - Guenter
02 -- folded into 01
03 -- Overlays, some times a good idea sometimes not. - Pantelis
04 -- Device Tree Documentation - Frank, Matt
05 -- Chat With The dtc Maintainers - Frank, the maintainers
06 -- Overlays and tools for sanity. - Pantelis
07 -- Device Tree Tools - Frank
08 -- Device Tree and parallel device probing - Pantelis
09 -- Device tree round up - Frank
     session  start
     length   offset
     ------   ------
  01    30       0
  02                 (folded into 01)
  03    15     :30
  04    15     :45
break   10    1:00
  05    30    1:10
  06    10    1:40
  07    15    1:55
  08    15    2:10
  09    10    2:20
      -----
       2:30
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

Category:

• Device
  tree