linux-kernel - Re: [RFC V6 2/3] arm:add bitrev.h file to support rbit instruction

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Date:	Wed, 14 Jan 2015 16:38:00 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
Cc:	'Ard Biesheuvel' <ard.biesheuvel@...aro.org>,
	'Will Deacon' <will.deacon@....com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'akinobu.mita@...il.com'" <akinobu.mita@...il.com>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>,
	'Joe Perches' <joe@...ches.com>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC V6 2/3] arm:add bitrev.h file to support rbit instruction

On Fri, Jan 09, 2015 at 08:40:56PM +0800, Wang, Yalin wrote:
> Oh, I see,
> How about change like this:
> +	select HAVE_ARCH_BITREVERSE if ((CPU_V7M || CPU_V7) && !CPU_V6 && !CPU_V6K)
> I am not sure if I also need add some older CPU types like !CPU_ARM9TDMI &&　!CPU_ARM940T ?
> 
> Another solution is:
> +	select HAVE_ARCH_BITREVERSE if ((CPU_32V7M || CPU_32V7) && !CPU_32V6 && !CPU_32V5 && !CPU_32V4 && !CPU_32V4T && !CPU_32V3)
> 
> By the way, I am not clear about the difference between CPU_V6 and CPU_V6K, could you tell me? :)

I think

	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6

is sufficient - we don't support mixing pre-v6 and v6+ CPU architectures
into a single kernel.

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