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

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Date:	Fri, 9 Jan 2015 11:10:48 +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 10:16:32AM +0800, Wang, Yalin wrote:
> > -----Original Message-----
> > From: Russell King - ARM Linux [mailto:linux@....linux.org.uk]
> > Sent: Friday, January 09, 2015 2:41 AM
> > To: Wang, Yalin
> > Cc: 'Will Deacon'; 'Ard Biesheuvel'; 'linux-kernel@...r.kernel.org';
> > 'akinobu.mita@...il.com'; 'linux-mm@...ck.org'; 'Joe Perches'; 'linux-arm-
> > kernel@...ts.infradead.org'
> > Subject: Re: [RFC V6 2/3] arm:add bitrev.h file to support rbit instruction
> > 
> > The root cause is that the kernel being built is supposed to support both
> > ARMv7 and ARMv6K CPUs.  However, "rbit" is only available on
> > ARMv6T2 (thumb2) and ARMv7, and not plain ARMv6 or ARMv6K CPUs.
> > 
> In the patch that you applied:
> 8205/1 	add bitrev.h file to support rbit instruction
> 
> I have add :
> +	select HAVE_ARCH_BITREVERSE if ((CPU_V7M || CPU_V7) && !CPU_V6)
> 
> If you build kernel support ARMv6K, should CONFIG_CPU_V6=y, isn't it ?
> Then will not build hardware rbit instruction, isn't it ?

The config has:

CONFIG_CPU_PJ4=y
# CONFIG_CPU_V6 is not set
CONFIG_CPU_V6K=y
CONFIG_CPU_V7=y
CONFIG_CPU_32v6=y
CONFIG_CPU_32v6K=y
CONFIG_CPU_32v7=y

And no, the CONFIG_CPU_V* flags refer to the CPUs.  The
CONFIG_CPU_32v* symbols refer to the CPU architectures.

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