linux-kernel - Re: [PATCH] OMAP: MMC: recover from transfer failures

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Date:	Sun, 8 Feb 2009 12:27:03 -0800
From:	David Brownell <david-b@...bell.net>
To:	Paul Walmsley <paul@...an.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jean Pihet <jpihet@...sta.com>, tony@...mide.com,
	ext-adrian.hunter@...ia.com,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-omap@...r.kernel.org, jarkko.lavinen@...ia.com,
	drzeus-mmc@...eus.cx, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] OMAP: MMC: recover from transfer failures - Resend

On Thursday 05 February 2009, Paul Walmsley wrote:
> 
> > > +   while (OMAP_HSMMC_READ(host->base,
> > > +                   SYSCTL) & SRD)
> > > +           ;
> > 
> > Is a __raw_readl() sufficient to prevent the cpu from burning up here,
> > or should we add cpu_relax()?
> 
> The __raw_readl() should be sufficient.  The MMC controller is located on 
> the L4 CORE interconnect, so the round trip latency for the read from MMC 
> is at least 90 ns, while the CPU cycle time is only about 1 to 2 ns.

It's still good policy to have a cpu_relax() in
such loops.  Not that it'll do much on most ARMs,
but empty statements are in general worth avoiding.


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