Device tree future

Devicetree Specification
The [[Media:Power_ePAPR_APPROVED_v1.1.pdf | Power.org Standard for Embedded Power Architecture Platform Requirements (ePAPR) v1.1]] is being updated, with the new name of Devicetree Specification Documentation.

[[Media:Devicetree_specification_linaro_connect_bangkok_2016.pdf|PDF presentation]] of the plans for the specification organization and the proposed schedule.

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.


 * 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
 * [[Media:petazzoni-device-tree-dummies_0.pdf|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
 * [[Media:Dynamic-dt-keynote-v3.pdf|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

Probe Ordering

 * Alexander Holler
 * 2014.05.12 [RFC PATCH 0/9 dt: dependencies (for deterministic driver]
 * Tomeu Vizoso
 * 2015.05.25[PATCH 00/21 On-demand device registration]
 * 2015.06.17 [PATCH 00/13 Discover and probe dependencies]
 * 2015.07.28 [PATCH v2 0/22 On-demand device probing]
 * 2015.08.06 [PATCH v3 0/18 On-demand device probing]
 * 2015.08.06 [PATCH v3 0/18 On-demand device probing (2nd archive)]

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
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

presentation material - at the conference

 * [[Media:Plumbers_2016_dt_schedule.pdf | schedule (PDF) - Frank Rowand]]
 * [[Media:Plumbers_2015_dt_DT-plumbers-2015.pdf | Dynamic DT and tools (pdf) - Pantelis Antoniou]]
 * [[Media:Plumbers_2016_dt_Devicetree_Overlays_at_Juniper.pdf | Device Tree Overlay use at Juniper Networks (PDF) - Guenter Roeck]]
 * [[Media:Plumbers_2016_dt_DT_Binding_Documentation.pdf | DT Binding Documentation (PDF) - Matt Porter]]
 * [[Media:Plumbers_2016_dt_device_tree_doc.pdf | Device Tree Documentation (PDF) - Frank Rowand]]
 * [[Media:Plumbers_2016_dt_device_tree_tools.pdf | Device Tree Tools (PDF) - Frank Rowand]]

etherpad notes - at the conference
https://etherpad.openstack.org/p/LPC2015_Device_Tree