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 10:16:32 +0800
From:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>
To:	'Russell King - ARM Linux' <linux@....linux.org.uk>
CC:	'Will Deacon' <will.deacon@....com>,
	'Ard Biesheuvel' <ard.biesheuvel@...aro.org>,
	"'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

> -----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
> 
> On Mon, Nov 17, 2014 at 10:38:58AM +0800, Wang, Yalin wrote:
> > Joe has submitted patches to maintainers, So we need wait for them to
> > be accepted .
> 
> I ran these patches through my autobuilder, and while most builds didn't
> seem to be a problem, the randconfigs found errors:
> 
> /tmp/ccbiuDjS.s:137: Error: selected processor does not support ARM mode
> `rbit r3,r2'
> /tmp/ccbiuDjS.s:145: Error: selected processor does not support ARM mode
> `rbit r0,r1'
> make[4]: *** [drivers/iio/amplifiers/ad8366.o] Error 1
> 
> /tmp/ccFhnoO3.s:6789: Error: selected processor does not support ARM mode
> `rbit r2,r2'
> make[4]: *** [drivers/mtd/devices/docg3.o] Error 1
> 
> /tmp/cckMf2pp.s:239: Error: selected processor does not support ARM mode
> `rbit ip,ip'
> /tmp/cckMf2pp.s:241: Error: selected processor does not support ARM mode
> `rbit r2,r2'
> /tmp/cckMf2pp.s:248: Error: selected processor does not support ARM mode
> `rbit lr,lr'
> /tmp/cckMf2pp.s:250: Error: selected processor does not support ARM mode
> `rbit r3,r3'
> make[5]: *** [drivers/video/fbdev/nvidia/nvidia.o] Error 1
> 
> /tmp/ccTgULsO.s:1151: Error: selected processor does not support ARM mode
> `rbit r1,r1'
> /tmp/ccTgULsO.s:1158: Error: selected processor does not support ARM mode
> `rbit r0,r0'
> /tmp/ccTgULsO.s:1164: Error: selected processor does not support ARM mode
> `rbit ip,ip'
> /tmp/ccTgULsO.s:1166: Error: selected processor does not support ARM mode
> `rbit r3,r3'
> /tmp/ccTgULsO.s:1227: Error: selected processor does not support ARM mode
> `rbit r5,r5'
> /tmp/ccTgULsO.s:1229: Error: selected processor does not support ARM mode
> `rbit lr,lr'
> /tmp/ccTgULsO.s:1236: Error: selected processor does not support ARM mode
> `rbit r0,r0'
> /tmp/ccTgULsO.s:1238: Error: selected processor does not support ARM mode
> `rbit r3,r3'
> make[5]: *** [drivers/video/fbdev/nvidia/nv_accel.o] Error 1
> 
> 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 ?

Thanks








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