linux-kernel - Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.

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Message-ID: <AANLkTinRM3_kBc5S3wV=_S6P8+x7A43kz0qSYbixJYnq@mail.gmail.com>
Date:	Tue, 21 Sep 2010 16:47:45 -0400
From:	Kyle Moffett <kyle@...fetthome.net>
To:	John Stultz <johnstul@...ibm.com>
Cc:	Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	Krzysztof Halasa <khc@...waw.pl>,
	Rodolfo Giometti <giometti@...ux.it>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/5] ptp: Added a brand new class driver for ptp clocks.

On Fri, Aug 27, 2010 at 18:30, John Stultz <johnstul@...ibm.com> wrote:
> On one side, there is the view that the kernel should abstract and hide
> the hardware details to increase app portability. And the other is that
> the raw hardware details should be exposed, so the OS stays out of the
> way.
>
> Neither of these views are always right. Ideally we can come up with a
> abstracted way to provide the hardware data needed that's generic enough
> that applications don't have to be changed when moving between hardware
> or configurations.
>
> The posix clock id interface is frustrating because the flat static
> enumeration is really limiting.
>
> I wonder if a dynamic enumeration for posix clocks would be possibly a
> way to go?

Well how about something much more straightforward:

#define CLOCK_FD 0x80000000
fd = open("/dev/clocks/some_clock_name", O_RDONLY);
clock_gettime(CLOCK_FD | fd, &ts);

This would provide all of the standard character-device semantics that
everyone is accustomed to, and furthermore you could allow non-root
users to manage specific clocks using just DAC permission bits.

You'd still probably need to add a clock_adjtimex() syscall, but it
could easily fail with EINVAL for software or per-thread clocks, but
that seems like it would nicely abstract the hardware without forcing
a numeric address space.

Cheers,
Kyle Moffett
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