netdev - Re: [PATCH v3 08/10] ARM: mxs: add ocotp read function

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Date:	Wed, 5 Jan 2011 17:25:01 +0000
From:	Jamie Iles <jamie@...ieiles.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Jamie Iles <jamie@...ieiles.com>,
	Shawn Guo <shawn.guo@...escale.com>, gerg@...pgear.com,
	B32542@...escale.com, netdev@...r.kernel.org,
	s.hauer@...gutronix.de, baruch@...s.co.il, w.sang@...gutronix.de,
	r64343@...escale.com, eric@...rea.com, bryan.wu@...onical.com,
	davem@...emloft.net, linux-arm-kernel@...ts.infradead.org,
	lw@...o-electronics.de
Subject: Re: [PATCH v3 08/10] ARM: mxs: add ocotp read function

On Wed, Jan 05, 2011 at 05:44:09PM +0100, Uwe Kleine-König wrote:
> Hello Jamie,
> On Wed, Jan 05, 2011 at 04:16:46PM +0000, Jamie Iles wrote:
> > On Wed, Jan 05, 2011 at 10:07:35PM +0800, Shawn Guo wrote:
> > > +	/* check both BUSY and ERROR cleared */
> > > +	while ((__raw_readl(ocotp_base) &
> > > +		(BM_OCOTP_CTRL_BUSY | BM_OCOTP_CTRL_ERROR)) && --timeout)
> > > +		/* nothing */;
> > 
> > Is it worth using cpu_relax() in these polling loops?
> I don't know what cpu_relax does for other platforms, but on ARM it's
> just a memory barrier which AFAICT doesn't help here at all (which
> doesn't need to be correct).  Why do you think it would be better?

Well I don't see that there's anything broken without cpu_relax() but 
using cpu_relax() seems to be the most common way of doing busy polling 
loops that I've seen. It's also a bit easier to read than a comment and 
semi-colon. Perhaps it's just personal preference.

Jamie
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