netdev - Re: [PATCH v6 0/8] ptp: IEEE 1588 hardware clock support

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Date:	Fri, 24 Sep 2010 15:57:13 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	john stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, linux-api@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 0/8] ptp: IEEE 1588 hardware clock support

> > Instead, I think having the id hanging off the class driver is much
> > better, as it allows mapping the actual hardware to the id more clearly.
> > 
> > So I'd drop the "timesource" listing. And maybe change "id" to
> > "clock_id" so its a little more clear what the id is for.
> 
> Okay, I will drop /sys/class/timesource (hope Alan Cox agrees :)

It makes sense to hang anything off the physical id

> I threw it out there mostly for the sake of discussion. I imagined
> that there could be other properties in that directory, like time
> scale (TAI, UTC, etc). But it seems like we don't really need anything
> in that direction.

They can still hang off the physical device. Thats really a detail

> > interrupts are awfully frequent, so systems concerned with power-saving
> > and deep idles probably would like something that could be done at a
> > more coarse interval.
> 
> We could always make the pulse rate programmable, for power-saving
> applications.

I would expect the kernel drivers to be responsible for
- Turning off when they can
- Picking rates that are power optimal for the requirement

The latter is a bit interesting as I don't see anything in any of the
timer APIs to express accuracy (a problem we have in kernel too).
Historically it simply hasn't mattered.
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