sysfs-bus-pci-drivers-ehci_hcd 1.8 KB

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  1. What: /sys/bus/pci/drivers/ehci_hcd/.../companion
  2. /sys/bus/usb/devices/usbN/../companion
  3. Date: January 2007
  4. KernelVersion: 2.6.21
  5. Contact: Alan Stern <stern@rowland.harvard.edu>
  6. Description:
  7. PCI-based EHCI USB controllers (i.e., high-speed USB-2.0
  8. controllers) are often implemented along with a set of
  9. "companion" full/low-speed USB-1.1 controllers. When a
  10. high-speed device is plugged in, the connection is routed
  11. to the EHCI controller; when a full- or low-speed device
  12. is plugged in, the connection is routed to the companion
  13. controller.
  14. Sometimes you want to force a high-speed device to connect
  15. at full speed, which can be accomplished by forcing the
  16. connection to be routed to the companion controller.
  17. That's what this file does. Writing a port number to the
  18. file causes connections on that port to be routed to the
  19. companion controller, and writing the negative of a port
  20. number returns the port to normal operation.
  21. For example: To force the high-speed device attached to
  22. port 4 on bus 2 to run at full speed::
  23. echo 4 >/sys/bus/usb/devices/usb2/../companion
  24. To return the port to high-speed operation::
  25. echo -4 >/sys/bus/usb/devices/usb2/../companion
  26. Reading the file gives the list of ports currently forced
  27. to the companion controller.
  28. Note: Some EHCI controllers do not have companions; they
  29. may contain an internal "transaction translator" or they
  30. may be attached directly to a "rate-matching hub". This
  31. mechanism will not work with such controllers. Also, it
  32. cannot be used to force a port on a high-speed hub to
  33. connect at full speed.
  34. Note: When this file was first added, it appeared in a
  35. different sysfs directory. The location given above is
  36. correct for 2.6.35 (and probably several earlier kernel
  37. versions as well).