> So then, when I "eject" an USB device in M$ Windows, what actually happens is
> not a "power off"
> the device, but a "suspend" the device ?
What happens when you throw a USB bus monitor on it? They probably would
at least quiesce all the drivers using the device and suspend and/or disable
that device's port, but they might also power it off if the hub allows. The
downside of powering down that port is that most USB hardware doesn't then
know how to report device connection. (The OTG "Session Request Protocol"
would do it, but most non-OTG hardware doesn't support it.)
> Is there any way I can tell if my USB controller is able to power off or not ?
> Can it be seen in the output of the lsusb -v ? Or in some /sys files ?
Current versions of "lsusb -v" will indeed show hub descriptors, if you
invoke them as root. At the end of the listing for the hub device you
will see the hub descriptor and status, as appended below.
- Dave
Hub Descriptor:
bLength 9
bDescriptorType 41
nNbrPorts 3
wHubCharacteristic 0x0002
No power switching (usb 1.0)
Ganged overcurrent protection
bPwrOn2PwrGood 1 * 2 milli seconds
bHubContrCurrent 0 milli Ampere
DeviceRemovable 0x55 <-- bizarre
PortPwrCtrlMask 0x24 <-- ditto
Hub Port Status:
Port 1: 0000.0100 power
Port 2: 0000.0100 power
Port 3: 0000.0100 power
Device Status: 0x0001
Self Powered
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