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    SubjectRE: PROBLEM: kernel oops with g_serial USB gadget on 2.6.30
    Hello, 

    On Tuesday, June 23, 2009 9:23 AM, David Brownell wrote:

    > > > Like, oh, changing a spinlock to a mutex.   You might change the
    > > > low_latency setting and review how that's now supposed to behave.
    > >
    > > In in gs_open() function in drivers/usb/gadget/u_serial.c, after the
    > > line 780 I've added:
    > >
    > > tty->low_latency = 1;
    >
    > That's already how it's set. Try instead *REMOVING* the line
    > which sets that flag.

    My fault. I didn't notice that a few lines lower the low_latency flag is
    alredy set and I thought I should set it. After removing that, g_serial
    started working. :) Thanks a lot.

    I noticed that there is also a comment:
    /* low_latency means ldiscs work in tasklet context, without
    * needing a workqueue schedule ... easier to keep up.
    */

    So in low latency mode calls are made from a tasklet. This is not true in
    my case, as the S3C OTG UDC driver does all its job in interrupts. This
    way also a (usb) packet_done callback is done from an interrupt. I expect
    that g_serial driver interacts with tty layer in that packet_done callback,
    so this is the source of the problems. I noticed that some other UDC
    drivers also does all its job from an interrupt, so they also might be
    affected. How this bug should be properly resolved?

    Best regards
    --
    Marek Szyprowski
    Samsung Poland R&D Center


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