From: Alan Stern Date: Wed, 14 Sep 2011 16:33:16 +0000 (-0400) Subject: USB: document ehci-hcd's "companion" sysfs attribute X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=25aa55488c3644b19e33ba79c564191b8e33f477;p=openwrt%2Fstaging%2Fblogic.git USB: document ehci-hcd's "companion" sysfs attribute This patch (as1484) adds documentation for ehci-hcd's "companion" sysfs attribute, which was added to the kernel over four years ago but never documented. Signed-off-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd new file mode 100644 index 000000000000..60c60fa624b2 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-ehci_hcd @@ -0,0 +1,46 @@ +What: /sys/bus/pci/drivers/ehci_hcd/.../companion + /sys/bus/usb/devices/usbN/../companion +Date: January 2007 +KernelVersion: 2.6.21 +Contact: Alan Stern +Description: + PCI-based EHCI USB controllers (i.e., high-speed USB-2.0 + controllers) are often implemented along with a set of + "companion" full/low-speed USB-1.1 controllers. When a + high-speed device is plugged in, the connection is routed + to the EHCI controller; when a full- or low-speed device + is plugged in, the connection is routed to the companion + controller. + + Sometimes you want to force a high-speed device to connect + at full speed, which can be accomplished by forcing the + connection to be routed to the companion controller. + That's what this file does. Writing a port number to the + file causes connections on that port to be routed to the + companion controller, and writing the negative of a port + number returns the port to normal operation. + + For example: To force the high-speed device attached to + port 4 on bus 2 to run at full speed: + + echo 4 >/sys/bus/usb/devices/usb2/../companion + + To return the port to high-speed operation: + + echo -4 >/sys/bus/usb/devices/usb2/../companion + + Reading the file gives the list of ports currently forced + to the companion controller. + + Note: Some EHCI controllers do not have companions; they + may contain an internal "transaction translator" or they + may be attached directly to a "rate-matching hub". This + mechanism will not work with such controllers. Also, it + cannot be used to force a port on a high-speed hub to + connect at full speed. + + Note: When this file was first added, it appeared in a + different sysfs directory. The location given above is + correct for 2.6.35 (and probably several earlier kernel + versions as well). +