linux-kernel - Re: [PATCH v4 2/5] arm: add new asm macro update

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Date:	Mon, 3 Feb 2014 16:00:51 +0000
From:	Will Deacon <will.deacon@....com>
To:	Leif Lindholm <leif.lindholm@...aro.org>
Cc:	"msalter@...hat.com" <msalter@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"patches@...aro.org" <patches@...aro.org>,
	"roy.franz@...aro.org" <roy.franz@...aro.org>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 2/5] arm: add new asm macro update_sctlr

On Mon, Feb 03, 2014 at 03:55:42PM +0000, Leif Lindholm wrote:
> On Mon, Feb 03, 2014 at 10:34:15AM +0000, Will Deacon wrote:
> > On Thu, Jan 30, 2014 at 01:12:47PM +0000, Leif Lindholm wrote:
> > > Oh, that's neat - thanks!
> > > 
> > > Well, given that, I can think of two less horrible options:
> > > 1)
> > > 	.macro  update_sctlr, tmp:req, set=, clear=
> > >         mrc	p15, 0, \tmp, c1, c0, 0
> > > 	.ifnc	\set,
> > >         orr	\tmp, \set
> > > 	.endif
> > > 	.ifnc	\clear,
> > > 	mvn	\clear, \clear
> > > 	and	\tmp, \tmp, \clear
> > 
> > Can't you use bic here?
> 
> Yeah.
> 
> > > 	.endif
> > >         mcr	p15, 0, \tmp, c1, c0, 0
> > > 	.endm
> > > 
> > > With the two call sites in uefi_phys.S as:
> > > 
> > > 	ldr	r5, =(CR_M)
> > > 	update_sctlr	r12, , r5
> > > and
> > > 	ldr	r4, =(CR_I | CR_C | CR_M)
> > > 	update_sctlr	r12, r4
> > 
> > These ldr= could be movs, right?
> 
> The first one could.
> The second one could be movw on armv7+.
> 
> > If so, I definitely prefer this to putting an ldr = into the macro itself
> > (option 2).
> 
> And your preference between 1) and 2) is?

(1), using bic and mov[tw] where possible.

Will
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