[sane-devel] sane to work with USB 3.0

m. allan noah kitno455 at gmail.com
Tue Dec 2 02:44:36 UTC 2014

Ha! As we speak, I am digging into USB3 again, because command
counting seems to not fix every case. I will try your patch and report


On Mon, Dec 1, 2014 at 9:21 PM, Olaf Meeuwissen
<olaf.meeuwissen at avasys.jp> wrote:
> Olaf Meeuwissen writes:
>> m. allan noah writes:
>>> I have added a USB3 port to my computer, and have spent a few days
>>> investigating this problem.
>> I haven't had that kind of time, yet :-(
> Finally got time to do so.
> # Someone managed to sky-rocket the priority of USB3 support to the top
> # of my TODO list ;-)
>>> It seems to be a bug in Linux kernel related to a bookkeeping error
>>> when the USB device is closed.  [...]
> Based on two days of looking at USB3 behaviour with three EPSON scanners
> and three backends, that does not seem to be the whole story.
>>> I have committed these changes to sane-backends git repo in
>>> 7a590f362e7e93979b706dd9e6ae34584e926ec3. If users of fujitsu scanners
>>> could try it out, I would appreciate any feedback. Note that this does
>>> not fix USB3 problems in other sane backends. Until the kernel is
>>> fixed, these types of repairs will have to be made on a per-backend
>>> basis, at the discretion of the maintainer.
> The epson and epson2 backends have been and still are using the kind of
> command counting and making sure to send an even count of reads and
> writes you added to the fujitsu backend.  That notwithstanding, they
> suffer from USB3 I/O problems with the Perfection V700 (GT-X900) and
> ES-H300 (GT-2500).  The epkowa backend does *not* even up the reads and
> writes and unsurprisingly shows the same problems.  In addition, the
> GT-D1000 (GT-1500), a non-free plugin needing device, is also affected.
> Making the epkowa backend even up the reads and writes did *not* fix the
> problem.  What did fix the problem for all three scanners and all three
> backends for me was a tiny change in sanei_usb.c.  With that change, the
> evening up of reads and writes was not needed either.
> The sanei_usb.c code unconditionally sets the USB configuration.  This
> happens even if the device has only one.  I found that *not* setting the
> USB configuration when there is only one fixed all my USB3 problems.  My
> understanding of the USB2 and USB3 standards is that the default USB
> configuration has to be set before devices become available to libusb.
> If that understanding is correct, then there is no need to set it unless
> you need a configuration that *differs* from the current one.  With only
> one configuration to choose from, there is then no need to set it.
> This patch does exactly that.  It skips setting the USB configuration if
> there is only one.  It should not break USB for any of the backends and
> *may* fix USB3 for all of them.
> Note: it may still set the default configuration if there are multiple
>       ones to choose from.  I have no devices I can test with to see if
>       that is problematic or not.  Even so, modifying the code to only
>       set a USB configuration if it differs should be safe.
>       # Patch is in preparation.
> Allan, can you locally revert your fujitsu fixes and try with the patch
> I applied?  Does that fix your USB3 issues?  Do you still need to even
> up the reads and writes?
> Unless it breaks things for you, could you please commit my patch?
> # Even if it does not fix USB3 for you.
> Other people with USB3 issues are of course more than welcome to try
> this patch too!
>> [...]
> Hope this helps,
> --
> Olaf Meeuwissen, LPIC-2           FLOSS Engineer -- AVASYS CORPORATION
> FSF Associate Member #1962               Help support software freedom
>                  http://www.fsf.org/jf?referrer=1962

"well, I stand up next to a mountain- and I chop it down with the edge
of my hand"

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