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

[Wang, Yalin]

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx]
> Sent: Friday, January 09, 2015 7:11 PM
> To: Wang, Yalin
> Cc: 'Ard Biesheuvel'; 'Will Deacon'; 'linux-kernel@xxxxxxxxxxxxxxx';
> 'akinobu.mita@xxxxxxxxx'; 'linux-mm@xxxxxxxxx'; 'Joe Perches'; 'linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx'
> 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@xxxxxxxxxxxxxxxx]
> > > Sent: Friday, January 09, 2015 2:41 AM
> > > To: Wang, Yalin
> > > Cc: 'Will Deacon'; 'Ard Biesheuvel'; 'linux-kernel@xxxxxxxxxxxxxxx';
> > > 'akinobu.mita@xxxxxxxxx'; 'linux-mm@xxxxxxxxx'; 'Joe Perches';
> > > 'linux-arm- kernel@xxxxxxxxxxxxxxxxxxx'
> > > 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 







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