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    SubjectRe: [PATCH] RTC: Add mmap method to rtc character driver
    On Tue, Jul 25, 2006 at 07:57:30PM +0200, Segher Boessenkool wrote:
    > > At OLS last week, During Dave Jones Userspace Sucks presentation, Jim
    > >Geddys and some of the Xorg guys noted that they would be able to
    > >stop using gettimeofday
    > >so frequently, if they had some other way to get a millisecond
    > >resolution timer
    > >in userspace, one that they could perhaps read from a memory mapped
    > >page. I was
    > >right behind them and though that seemed like a reasonable
    > >request, so I've
    > >taken a stab at it. This patch allows for a page to be mmaped
    > >from /dev/rtc
    > >character interface, the first 4 bytes of which provide a regularly
    > >increasing
    > >count, once every rtc interrupt. The frequency is of course
    > >controlled by the
    > >regular ioctls provided by the rtc driver. I've done some basic
    > >testing on it,
    > >and it seems to work well.
    > Similar functionality is already available via VDSO on
    > platforms that support it (currently PowerPC and AMD64?) --
    > seems like a better way forward.
    In general I agree, but that only works if you operate on a platform that
    supports virtual syscalls, and has vdso configured. I'm not overly familiar
    with vdso, but I didn't think vdso could be supported on all platforms/arches.
    This seems like it might be a nice addition in those cases.


    > Segher

    *Neil Horman
    *Software Engineer
    *gpg keyid: 1024D / 0x92A74FA1 -
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