From mboxrd@z Thu Jan  1 00:00:00 1970
From: u.kleine-koenig@pengutronix.de (Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=)
Date: Mon, 14 Jun 2010 11:43:10 +0200
Subject: [RFC,PATCH 1/2] Add a common struct clk
In-Reply-To: <19477.63136.664249.167207@ipc1.ka-ro>
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>
Message-ID: <20100614094310.GE12159@pengutronix.de>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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/  |