linux-kernel - Re: [PATCHv2 1/3] ARM: Translate delay.S into (mostly) C

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Message-ID: <1288826235.16859.38.camel@c-dwalke-linux.qualcomm.com>
Date:	Wed, 03 Nov 2010 16:17:15 -0700
From:	Daniel Walker <dwalker@...eaurora.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Will Deacon <will.deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	Nicolas Pitre <nico@...xnic.net>,
	Kevin Hilman <khilman@...prootsystems.com>,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Saravana Kannan <skannan@...eaurora.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Colin Cross <ccross@...roid.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv2 1/3] ARM: Translate delay.S into (mostly) C

On Wed, 2010-11-03 at 16:15 -0700, Stephen Boyd wrote:
> On 11/03/2010 11:27 AM, Will Deacon wrote:
> > Hi Stephen,
> >
> > On Thu, 2010-10-28 at 21:19 +0000, Stephen Boyd wrote:
> >> Nico expressed concern that fixed lpj cmdlines will break due to
> >> compiler optimizations. That doesn't seem to be the case since
> >> before and after this patch I get the same lpj value when running
> >> my CPU at 19.2 MHz. That should be sufficiently slow enough to
> >> cover any machine running Linux.
> >
> > I appreciate this is an exceptional case, but there are some lucky
> > guys at ARM who (as routinely as they can) boot Linux on sub 1MHz
> > hardware. The delay loop is something they're keen to avoid so they do
> > make use of the lpj= command line option and would rather it didn't
> > break on them.
> 
> Do you know if it breaks at that frequency? I don't have any hardware to
> test with that goes lower than the stated 19.2 MHz.

Isn't it possible that a new compiler could optimize the code
differently, and then end up breaking lpj= ?

Daniel

-- 

Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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