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

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Date:	Mon, 3 Feb 2014 10:20:09 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Leif Lindholm <leif.lindholm@...aro.org>,
	"roy.franz@...aro.org" <roy.franz@...aro.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"msalter@...hat.com" <msalter@...hat.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 3, 2014 at 10:00 AM, Will Deacon <will.deacon@....com> wrote:
> 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.

Using mov[tw] will break on V6 enabled builds.

Rob
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