Re: [PATCH] RTC: Add mmap method to rtc character driver

Segher Boessenkool
2006-07-25T17:57:35Z

> 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.

Segher