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    SubjectRe: Enable CONFIG_USB_SUSPEND by default or some mobile HD can't be unplugged safely
    On Fri, 2 Jan 2009, Yan Li wrote:

    > Now I know 3 methods supposed can be used to shut the device:
    > 1. (Alan Stern said Windows use this) cut the USB port's power

    I said no such thing! In fact, I said exactly the opposite: Windows
    does _not_ cut the port's power. Instead it disables the port.

    > 2. send STOP SCSI command to stop it

    Note that this is different. The START-STOP command is used to spin-up
    or spin-down a disk. It does not affect the state of the data link.

    > 3. put it into suspend mode

    As far as the device is concerned, there is essentially no difference
    between 1 and 3. When the device's upstream port is disabled, the
    device must go into suspend mode.

    The best approach is to send a SYNCHRONIZE CACHE command followed by
    START-STOP (if the device supports it), and then to disable or suspend
    the port. In Linux, those two commands will be sent automatically if
    you unbind the device from usb-storage. The suspend has to be done
    manually unless you have set up a udev rule (or something equivalent)
    to enable autosuspend for the device. Of course, this requires
    CONFIG_USB_SUSPEND.

    Alan Stern



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