This document summarizes a presentation about the ACPI device tree and hot removal in Linux. It describes how the ACPI namespace is converted into a Linux device tree and updated upon hotplug events. It explains how ACPI devices can be linked to physical devices as companions. It also outlines the device ejection flow and how the ACPI hot removal path works, including using status codes.

1. ACPI device tree and hot
remove flow
April, 2017, SUSE Labs Taipei technology sharing day, Taipei
Joey Lee
SUSE Labs Taipei

2. 2
Agenda
• ACPI device tree and companion object
• ACPI hot remove
• Q&A

3. ACPI device tree

4. 4
ACPI namespace
• The data block of the DSDT along with the contents
of SSDTs represents a hierarchical data structure
called the ACPI namespace whose topology reflects
the structure of the underlying hardware platform. [1]

5. 5
ACPI device tree
• The Linux ACPI subsystem converts ACPI
namespace objects into a Linux device tree under
the /sys/devices/LNXSYSTEM:00 and updates it
upon receiving ACPI hotplug notification events. For
each device object in this hierarchy there is a
corresponding symbolic link in the
/sys/bus/acpi/devices. [1]

6. 6
ACPI device tree (cont.)

7. 7
ACPI device companion
• ACPI device (i.e. struct acpi_device) objects may be
linked to other objects in the Linux' device hierarchy
that represent "physical" devices (for example,
devices on the PCI bus). If that happens, it means
that the ACPI device object is a "companion" of a
device [1]

8. 8
ACPI device companion (cont.)

9. 9
Conceptual model of acpi device

10. 10
ACPI bus/device initial path

11. ACPI hot remove

12. 12
Device Ejection Flow Example
ACPI spec v6.1 [2]

13. 13
Memory ejection flow

14. 14
Handle containers

15. 15
ACPI container ejection flow

16. 16
ACPI hot remove path

17. 17
ACPI hot remove path – status code

18. Q&A

19. 19
Reference
• [1] Documentation/acpi/namespace.txt, Linux Kernel
• [2] Advanced Configuration and Power Interface
Specification, Version 6.1, Intel

20. Thank you.
20
Feedback to
jlee@suse.com

22. Corporate Headquarters
Maxfeldstrasse 5
90409 Nuremberg
Germany
+49 911 740 53 0 (Worldwide)
www.suse.com
Join us on:
www.opensuse.org
22

23. Unpublished Work of SUSE. All Rights Reserved.
This work is an unpublished work and contains confidential, proprietary and trade secret information of SUSE.
Access to this work is restricted to SUSE employees who have a need to know to perform tasks within the scope of
their assignments. No part of this work may be practiced, performed, copied, distributed, revised, modified, translated,
abridged, condensed, expanded, collected, or adapted without the prior written consent of SUSE.
Any use or exploitation of this work without authorization could subject the perpetrator to criminal and civil liability.
General Disclaimer
This document is not to be construed as a promise by any participating company to develop, deliver, or market a
product. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making
purchasing decisions. SUSE makes no representations or warranties with respect to the contents of this document,
and specifically disclaims any express or implied warranties of merchantability or fitness for any particular purpose. The
development, release, and timing of features or functionality described for SUSE products remains at the sole
discretion of SUSE. Further, SUSE reserves the right to revise this document and to make changes to its content, at
any time, without obligation to notify any person or entity of such revisions or changes. All SUSE marks referenced in
this presentation are trademarks or registered trademarks of Novell, Inc. in the United States and other countries. All
third-party trademarks are the property of their respective owners.