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

-----Original Message-----
From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
Sent: Friday, January 09, 2015 2:41 AM
To: Wang, Yalin
Cc: 'Will Deacon'; 'Ard Biesheuvel'; 'linux-kernel at vger.kernel.org';
'akinobu.mita at gmail.com'; 'linux-mm at kvack.org'; 'Joe Perches'; 'linux-arm-
kernel at lists.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:

quoted

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