linux-kernel - Re: LinuxPPS & spinlocks

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Message-ID:  <loom.20070802T000504-963@post.gmane.org>
Date:	Wed, 1 Aug 2007 22:14:54 +0000 (UTC)
From:	Christopher Hoover <ch@...gatroid.com>
To:	linux-kernel@...r.kernel.org
Subject:  Re: LinuxPPS & spinlocks

Satyam Sharma <satyam <at> infradead.org> writes:
> On Mon, 30 Jul 2007, Rodolfo Giometti wrote:
> 
> > On Mon, Jul 30, 2007 at 10:33:35AM +0530, Satyam Sharma wrote:
> > Currently the RFC says to you that you should open the serial port:
> > 
> > 	fd = open("/dev/ttyS0", ...);
> 
> No, it does *NOT*. All it says is:
> 
>     The time_pps_create() is used to convert an already-open UNIX file
>     descriptor, for an appropriate special file, into a PPS handle.
> 
> See? What I said is precisely the implementation the RFC envisages
> (and the only sane way to implement it too).

If we were totally rigurous about representing each device as a device node, 
your solution would be fine.  But we don't.

The clocksource model (/sys/devices/system/clocksource) is a better way to 
go.  One sysfs file is used to enumerate the possible sources and another is 
used to read or set the current source.   No new system calls; no new ioctls.

-ch

ch (at) murgatroid (dot) com
ch (at) hpl (dot) hp (dot) com




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