Date: Mon, 14 Jun 2010 11:43:10 +0200
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
	<u.kleine-koenig@pengutronix.de>
To: Lothar =?iso-8859-1?Q?Wa=DFmann?= <LW@KARO-electronics.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Jeremy Kerr <jeremy.kerr@canonical.com>,
       Ben Dooks <ben-linux@fluff.org>, linux-kernel@vger.kernel.org,
       linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC,PATCH 1/2] Add a common struct clk
Message-ID: <20100614094310.GE12159@pengutronix.de>
References: <201006111557.12249.jeremy.kerr@canonical.com> <19473.61547.684572.647641@ipc1.ka-ro> <201006111718.47426.jeremy.kerr@canonical.com> <19474.172.742782.972629@ipc1.ka-ro> <20100611095839.GC10894@pengutronix.de> <19474.2817.333749.485028@ipc1.ka-ro> <1276319643.1962.181.camel@pasglop> <19477.52889.982995.407051@ipc1.ka-ro> <1276507378.2552.39.camel@pasglop> <19477.63136.664249.167207@ipc1.ka-ro>
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On Mon, Jun 14, 2010 at 11:30:08AM +0200, Lothar Wa?mann wrote:
> Benjamin Herrenschmidt writes:
> > On Mon, 2010-06-14 at 08:39 +0200, Lothar Wa?mann wrote:
> > > All implementations so far use spin_lock_irq_save()!
> > 
> > Nothing prevents your implementation to be a tad smarter.
> > 
> I vote for consistency, so that device drivers can be kept arch
> independent instead of having to care about implentation details of
> each arch.
Back when I implemented clock support for ns9xxx (unfortunately not in
mainline) I tried with a spinlock first and later switched to a mutex.
IIRC the reason was that on ns9215 enabling the rtc clock took long
(don't remember a number) and successfull enabling was signaled by an
irq.  So I would have had to implement irq polling in the clock code.

I think you can find different examples that make both possiblities bad.
All in all I think that a sleeping clock implementation is preferable as
it improves (general) latencies.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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