From mboxrd@z Thu Jan  1 00:00:00 1970
From: jamie@jamieiles.com (Jamie Iles)
Date: Tue, 23 Aug 2011 10:53:54 +0100
Subject: [PATCH v2 1/4] ARM: CSR: add rtc i/o bridge interface for
	SiRFprimaII
In-Reply-To: <CAGsJ_4wpHBYuALijDWpLsmYTiDQddAW1DdE84tY=w4==eiyJhA@mail.gmail.com>
References: <1314080152-30503-1-git-send-email-Baohua.Song@csr.com>
	<1314080152-30503-2-git-send-email-Baohua.Song@csr.com>
	<20110823084819.GG2796@pulham.picochip.com>
	<CAGsJ_4wpHBYuALijDWpLsmYTiDQddAW1DdE84tY=w4==eiyJhA@mail.gmail.com>
Message-ID: <20110823095354.GK2796@pulham.picochip.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Aug 23, 2011 at 05:33:39PM +0800, Barry Song wrote:
> 2011/8/23 Jamie Iles <jamie@jamieiles.com>:
> > On Mon, Aug 22, 2011 at 11:15:49PM -0700, Barry Song wrote:
[...]
> >> +void sirfsoc_rtc_iobrg_wait_sync(void)
> >> +{
> >> + ? ? while (readl_relaxed(sirfsoc_rtciobrg_base + SIRFSOC_CPUIOBRG_CTRL))
> >> + ? ? ? ? ? ? continue;
> >
> > It might be worth using cpu_relax() here as it includes a memory barrier
> > that's what many busy wait loops do.
> 
> yes. generically people add a cpu_relax() in busy wait and that makes
> lots of senses. it seems readl_relaxed() can keep the execution
> sequence even without the barrier?

Well readl_relaxed() uses __raw_readl() which marks the dereference as 
volatile, so you should be okay without the cpu_relax() here.  Having 
said that, cpu_relax() is a little more explicit, so whatever you think 
most appropriate I guess.

Jamie