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    SubjectRe: SYSFS: need a noncaching read
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    Hello Greg

    Am Mittwoch, den 12.09.2007, 03:01 -0700 schrieb Greg KH:
    > On Wed, Sep 12, 2007 at 07:32:07AM +0200, Robert Schwebel wrote:
    > > On Tue, Sep 11, 2007 at 11:43:17AM +0200, Heiko Schocher wrote:
    > > > I have developed a device driver and use the sysFS to export some
    > > > registers to userspace.
    > >
    > > Uuuh, uggly. Don't do that. Device drivers are there to abstract things,
    > > not to play around with registers from userspace.
    > >
    > > > I opened the sysFS File for one register and did some reads from this
    > > > File, but I alwas becoming the same value from the register, whats not
    > > > OK, because they are changing. So I found out that the sysFS caches
    > > > the reads ... :-(
    > >
    > > Yes, it does. What you can do is close()ing the file handle between
    > > accesses, which makes it work but is slow.
    >
    > Do an lseek back to 0 and then re-read, you will get called in your
    > driver again.

    No thats not true. I thought this too, but if I make a:

    seek (fd, 0L, SEEK_SET);

    in Userspace, there is no retrigger in the sysFS, my driver is *not*
    called again. So I made a own sysfs_seek function, which does retrigger
    the driver ...

    Is this really wanted in the sysFS, that there is no way to retrigger a
    read?

    thanks
    Heiko
    --
    DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
    HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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