linux-kernel - Re: [PATCHv5 1/3] ARM: Translate delay.S into (mostly) C

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Date:	Thu, 7 Apr 2011 09:29:57 +0200
From:	Mattias Wallin <mattias.wallin@...ricsson.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCHv5 1/3] ARM: Translate delay.S into (mostly) C

On 04/06/2011 01:56 AM, Stephen Boyd wrote:
> We want to allow machines to override the __delay() implementation
> at runtime so they can use a timer based __delay() routine. It's
> easier to do this using C, so let's write udelay and friends in C.
>
> We lose the #if 0 code, which according to Russell is used "to
> make the delay loop more stable and predictable on older CPUs"
> (seehttp://article.gmane.org/gmane.linux.kernel/888867  for more
> info). We shouldn't be too worried though, since we'll soon add
> functionality allowing a machine to set the __delay() loop
> themselves, thus allowing machines to resurrect the commented out
> code should they need it.
>
> Nicolas 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.

Tested-by: Mattias Wallin <mattias.wallin@...ricsson.com>

Yours,
Mattias Wallin

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