Comment 394 for bug 85488

well, the sane developers seem to be working on this as well:
http://lists.alioth.debian.org/pipermail/sane-devel/2007-July/019680.html

quoted:
> Hi,
>
> CONFIG_USB_SUSPEND, a Linux kernel option that makes the USB layer
> automatically put USB devices to suspend state when they're not in
> use, has exposed a number of bugs in pretty much all the USB
> scanners.
>
> Upon being suspended, the scanners will usually do an unplug/plug
> cycle instead of going into the suspended state - what really happens
> in most cases is that the scanner resets himself, loosing its settings
> and sometimes its firmware. Some scanners may react differently,
> exposing more hardware bugs (eg. their USB interface may crash).
>
> Starting with Linux 2.6.22, two things have happened:
> - a blacklist for the autosuspend feature, in which a lot of scanners
> are being added, mainly by Oliver Neukum from what I've seen, has been
> added. As of 2.6.22, the blacklist only has 2 or 3 entries IIRC, and
> is already greatly expanded in Greg KH's git tree - so this will make
> it into 2.6.23. This blacklist alone is obviously not going to cut it;
> we've got rid of the scanner kernel module because it was painful to
> keep it up to date and to update it on user's machine every time we
> needed to add a USB ID. This blacklist is just the same thing.
>
> - a sysfs attribute has been added to USB devices that allows turning
> off the USB autosuspend feature on a per-device basis. This attribute
> can be found under /sys/bus/usb/devices/*/power/level.
>
>
> By doing echo on > /sys/bus/usb/devices/<device id>/power/level, it is
> possible to disable the USB autosuspend feature (and wake the scanner
> up if it's suspended).
>
> By doing echo suspend > /sys/bus/usb/devices/<device id>/power/level,
> it is possible to force a device into suspend mode (and it won't be
> waken up automatically).
>
> By doing echo auto > /sys/bus/usb/devices/<device id>/power/level, the
> default behaviour of automatically suspending the device can be
> restored.
>
>
> So, as of a few minutes ago, the udev rules generated by sane-desc
> include a new RUN rule that will disable the USB autosuspend feature
> for all the scanners we know.
>
>
> That's the end of "black scans" as long as you run a kernel >= 2.6.22
> and this sysfs interface doesn't change :-)
>
> Have fun,
>
> JB.

--
Clay Weber
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