The document discusses USB power management and how it can be improved. It explains that USB device suspend is often broken, but newer technologies like USB 3.0 link power management and features in Intel chips help address these issues. It provides resources for testing and enabling USB power management and outlines Sarah Sharp's presentation on improving USB suspend behavior.

1. Vampire Mice:
How USB
Power Management
Impacts You
Sarah Sharp
sarah.a.sharp@intel.com
Jan 25, 2013

2. Mouse: flickr.com rick-in-rio Software and Services Group (SSG)
2 Mouse: flickr.com 27048731@N03
System Software Division (SSD)

3. Mouse: flickr.com rick-in-rio Software and Services Group (SSG)
3 Mouse: flickr.com 27048731@N03
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4. Agenda
• How USB PM works
• ...and how it doesn't work
• New USB 3.0 and 2.1 features
• New features in Intel systems
Software and Services Group (SSG)
4 System Software Division (SSD)

5. How USB
Power Management
Works
Software and Services Group (SSG)
5 System Software Division (SSD) Lightbulb: flickr.com hozae

6. USB Power Management
• Three types of PM:
• USB device suspend
• USB host suspend
• Link Power Management
Software and Services Group (SSG)
6 Light bulb: flickr.com molotalk
System Software Division (SSD)

7. USB Device Suspend
• Devices suspended when
they're inactive
• Hubs suspend when
all children are suspended
• USB hosts suspend when
all ports are suspended
Software and Services Group (SSG)
7 System Software Division (SSD)

8. USB Device Suspend
• Implications of active USB host
• Active DMA transfers
• Increased C state residency
• Increased power consumption
Software and Services Group (SSG)
8 System Software Division (SSD)

9. USB Device Suspend
• USB device suspend requirements
• Device must support suspend
• Driver must support auto-suspend
• No active USB transfers
• Userspace can't poll
• Remote wakeup (optional)
Software and Services Group (SSG)
9 System Software Division (SSD)

10. How USB
Power Management
Doesn't Work
Software and Services Group (SSG)
10 System Software Division (SSD) Broken light bulb: flickr.com ginsnob

11. USB Device Suspend Issues
• Missing driver auto-suspend support
• Impossible to get to idle
• Userspace polls devices
Are we
there yet?
Is an SD card
inserted yet?
Software and Services Group (SSG)
11 SD card reader: flickr.com osde-info System Software Division (SSD)

12. USB Device Suspend Issues
• Many USB devices are broken
• Disconnect on resume
• Unsafe suspend behavior
• No remote wakeups
• Event loss during resume
• Firmware updates may help
• Device descriptors often
unchanged
Software and Services Group (SSG)
12 Mouse: flickr.com declanjewell System Software Division (SSD)

13. USB Device Suspend Issues
• Different systems produce
different behavior
• Electrical issues?
• Host hardware bugs?
• Powered USB hubs?
• Device driver bugs?
Software and Services Group (SSG)
13 dusty computer: flickr.com johnjack System Software Division (SSD)

14. USB Device Suspend Issues
• What to do about broken devices?
• Huge blacklist in kernel
• Make it userspace's problem!
• USB device suspend off by default
• Userspace must turn it on
• # echo auto >
/sys/bus/usb/devices/*/power/control
• Powertop can turn it on
Software and Services Group (SSG)
14 Blame: flickr.com iandesign System Software Division (SSD)

15. Turning on USB PM
Software and Services Group (SSG)
15 System Software Division (SSD)

16. Turning on USB PM
• Powertop auto-suspend enabling
doesn't persist across
• Device unplug
• Reboot
• Solution: create a udev rule
• github.com/sarahsharp/usb-pm-tools
Software and Services Group (SSG)
16 Boot: flickr.com jamiecat System Software Division (SSD)

17. USB Device Suspend
Takeaway:
All your USB devices
must be suspended
to get good platform
power management.
1. Test your devices.
2. Enable auto-suspend
Software and Services Group (SSG)
17 System Software Division (SSD)

18. USB
Link Power
Management
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18 System Software Division (SSD)

19. Challenges with
USB device suspend
• Users must turn it on
• Requires driver modification
• Timeout is course-grained
• Devices can't refuse suspend
Software and Services Group (SSG)
19 Blame: flickr.com iandesign System Software Division (SSD)

20. USB 3.0
Link Power Management
• USB 3.0 Link PM
• Link PM states: U1 and U2
• Idea:
• Host & hubs track idleness U1
• OS sets timeout once
• No driver modification
• Devices can refuse U1/U2
U2
U1
Software and Services Group (SSG)
20 System Software Division (SSD)

21. USB 3.0
Link Power Management
• Some USB 3.0 devices don't do Link PM
• How to tell?
# lsusb -v -d 1d6b:0003 | grep "Port [0-9]*"
Hub Port Status:
Port 1: 0000.02a0 5Gbps power Rx.Detect
Port 2: 0000.0243 5Gbps power U2 enable connect
Port 3: 0000.02a0 5Gbps power Rx.Detect
Port 4: 0000.02a0 5Gbps power Rx.Detect
Software and Services Group (SSG)
21 System Software Division (SSD)

22. USB 2.1 Link PM
• New 'L1' low power state
• No changes to USB 2.0 hubs
• Only for devices on roothub L0
L1
• Good for integrated devices
L0
L0
Software and Services Group (SSG)
22 System Software Division (SSD)

23. New Intel
USB PM Features
Software and Services Group (SSG)
23 System Software Division (SSD)

24. Current and Future
Intel Products
• Current gen:
• CPU: Ivy Bridge
• Chipset: Panther Point
• Next gen:
• CPU: Haswell
• Chipsets: Lynx Point
Panther: flickr.com tim_ellis Software and Services Group (SSG)
24 Lynx: flickr.com keithmwilliams System Software Division (SSD)

25. Intel USB PM
Improvements
• Panther Point
• Finally has xHCI host controller!
• Only four ports under xHCI
• Supports USB 3.0 Link PM
• Lynx Point
• All ports under xHCI
• Supports USB 3.0 and
USB 2.1 Link PM
Panther: flickr.com tim_ellis Software and Services Group (SSG)
25 Lynx: flickr.com keithmwilliams System Software Division (SSD)

26. Intel Lynx Point
USB PM Improvements
• Motivation
• Unused internal ports
• Unused internal USB devices
internal laptop: flickr novakreo Software and Services Group (SSG)
26 finger print scanner: flickr mikedent System Software Division (SSD)

27. Intel Lynx Point
USB PM Improvements
• Idea:
• Completely power off port
• Lose USB events:
• Disconnect
• Connect
• Remote wakeup events
internal laptop: flickr novakreo Software and Services Group (SSG)
27 finger print scanner: flickr mikedent System Software Division (SSD)

28. Summary
Software and Services Group (SSG)
28 System Software Division (SSD) www.threadless.com/product/2168/USB_Port

29. Summary
• USB device suspend is often broken
• Try powertop
• Check out github.com/sarahsharp/usb-pm-tools
• Link PM improvements
• New Intel USB PM features
• Thanks!
Software and Services Group (SSG)
29 System Software Division (SSD)

30. Questions?
sarah.a.sharp@
linux.intel.com
Software and Services Group (SSG)
30 System Software Division (SSD)