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    SubjectRe: [PATCH 6/8] Kconfig: no userspace I/O on s390.
    On Thu, May 03, 2007 at 10:36:14AM +0200, Martin Schwidefsky wrote:
    > On Wed, 2007-05-02 at 22:30 -0700, Greg KH wrote:
    > > > Hide the config menu for userspace I/O on s390.
    > >
    > > Why? Who says s390 can't have userspace I/O drivers someday?
    >
    > Theoretically yes, but in practice this is very unlikely to happen. Some
    > reasons why:
    > 1) There are only very few device drivers for s390, the few we need
    > we'll do as kernel space drivers
    > 2) The irq abstraction of uio is awkward. The irq handler uses a 32-bit
    > integer. On s390 each ccw device has it's own irq and ccw devices are
    > identified with a string "x.y.zzzz". Then there are devices that deliver
    > external interrupts where a 16-bit number is used to identify the
    > source. You could invent some mapping logic of a 32 bit integer to all
    > the possible interrupt sources but it doesn't really match.
    > 3) s390 doesn't use memory mapped i/o, you always need to execute a
    > privileged instruction to trigger activity on the device, e.g. ssch for
    > a ccw device, siga for qdio, nqap for crypto, ...
    >
    > So I have my doubts that we will ever see a uio driver for s390. If we
    > do we can unhide the config menu again.

    Ok, that's find, can you bounce me the patch that made this change
    again?

    thanks,

    greg k-h
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