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    SubjectRe: USB mass storage and ARM cache coherency
    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.
    > IMHO, Linux should have functions similar to the DMA API but for PIO
    > drivers (e.g. pio_map_single/pio_unmap_single) that non-coherent
    > architectures can define, otherwise being no-ops. Any thoughts?
    I would certainly be in favour of such a thing, particularly since on SH
    we often find ourselves with coherent PIO and non-coherent MMIO.

    This is however something that should be prototyped and submitted to
    linux-arch for discussion.

    > diff --git a/drivers/usb/host/isp1760-hcd.c b/drivers/usb/host/isp1760-hcd.c
    > index 27b8f7c..4d3eeee 100644
    > --- a/drivers/usb/host/isp1760-hcd.c
    > +++ b/drivers/usb/host/isp1760-hcd.c
    > @@ -18,6 +18,8 @@
    > #include <linux/uaccess.h>
    > #include <linux/io.h>
    > #include <asm/unaligned.h>
    > +#include <asm/cacheflush.h>
    > +#include <asm/memory.h>
    asm/memory.h isn't a portable header. If you are including it for
    virt_to_page(), linux/io.h should already bring that in via asm/io.h.
    If arm doesn't bring in virt_to_page() through its asm/io.h, then fix the
    headers there please.

    FWIW I used the same fix you came up with on r8a66597_hcd and it fixed up
    crashes we were seeing there, too.

     \ /
      Last update: 2010-02-02 07:41    [W:0.021 / U:34.680 seconds]
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