FW: [RFC V6 2/3 resend] 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 7:11 PM
To: Wang, Yalin
Cc: 'Ard Biesheuvel'; 'Will Deacon'; '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 Fri, Jan 09, 2015 at 10:16:32AM +0800, Wang, Yalin wrote:

quoted

quoted

-----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

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.

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? :)

Thank you