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    SubjectRe: USB mass storage and ARM cache coherency
    [CC Takashi]

    On Mon, Feb 01, 2010 at 05:29:14PM +0000, Catalin Marinas wrote:
    > On Fri, 2010-01-29 at 18:54 +0000, Matthew Dharm wrote:
    > > HOWEVER, I firmly believe that the cache-management functions belong with
    > > the driver that actually talks to the low-level hardware, as that's the
    > > only place where you can be 100% certain of what cache operations are
    > > needed. After all, I think someone is working on a USB-over-IP transport,
    > > and trying to manage cache at the usb-storage level in that scenario is
    > > just silly.
    > >
    > > So, let's put this in the HCD drivers and be done with it.
    >
    > The patch below is what fixes the I-D cache incoherency issues on ARM. I
    > don't particularly like the solution but it seems to be the only one
    > available.

    Thanks very much for working on this amazingly large problem!

    I took some time to add your patch to ehci-q.c / ohci-q.c
    (for my *hci-ssb.c ASUS WL-500gP v2), on my now _heavily_ patched-up 2.6.31.9,
    but _UNFORTUNATELY_ it kept locking up the same way as always when stopping
    playback despite being damn sure this time that this patch could have
    the potential to finally fix it ;)
    (I had to replace memory.h with page.h on my arch though, to fix the build)

    This is on MIPSEL (not one of my many ARM devices, unfortunately ;),
    with usb-audio, and the madplay process crashes in __bzero(),
    which strongly indicates cache coherency issues (other subsequent backtraces
    have lots of mmap and vma listed, see also my "snd_usb_audio OOPS on MIPSEL -
    is that the mmap issue?").

    Next thing I'll do is fire up gdb and get a good backtrace of the
    __bzero() address to find out which page handling in mpd exactly
    is hampered with crashes. This is now ~ the third patch that I applied
    on-the-go and that didn't help, so it's probably time to do
    some earnest analysis on what's really going on locally.

    Note that usb-storage itself does work on this platform though.

    Rather annoying to be so close (sound works) yet so far away,
    especially after all that USB host trouble I already had.

    Thanks a lot again,

    Andreas Mohr


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