[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, November 14, 2014 7:53 AM
To: Wang, Yalin

quoted

On Fri, Oct 31, 2014 at 01:42:44PM +0800, Wang, Yalin wrote:
This patch add bitrev.h file to support rbit instruction, so that we
can do bitrev operation by hardware.
Signed-off-by: Yalin Wang <redacted>
---
 arch/arm/Kconfig              |  1 +
 arch/arm/include/asm/bitrev.h | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 arch/arm/include/asm/bitrev.h

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index

89c4b5c..be92b3b 100644

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig

@@ -28,6 +28,7 @@ config ARM
 	select HANDLE_DOMAIN_IRQ
 	select HARDIRQS_SW_RESEND
 	select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)
+	select HAVE_ARCH_BITREVERSE if (CPU_V7M || CPU_V7)

Looking at this, this is just wrong.  Take a moment to consider what
happens if we build a kernel which supports both ARMv6 _and_ ARMv7 CPUs.
What happens if an ARMv6 CPU tries to execute an rbit instruction?

Is it possible to build a kernel that support both CPU_V6 and CPU_V7?
I mean in Kconfig, CPU_V6 = y and CPU_V7 = y ?
If there is problem like you said,
How about this solution:
select HAVE_ARCH_BITREVERSE if ((CPU_V7M || CPU_V7) && !CPU_V6)  

Second point (which isn't obvious from your submissions on-list) is that
you've loaded the patch system up with patches for other parts of the
kernel tree for which I am not responsible for.  As such, I can't take
those patches without the sub-tree maintainer acking them.  Also, the
commit text in those patches look weird:

6fire: Convert byte_rev_table uses to bitrev8

Use the inline function instead of directly indexing the array.

This allows some architectures with hardware instructions for bit reversals
to eliminate the array.

Signed-off-by: Joe Perches <(address hidden)>
Signed-off-by: Yalin Wang <(address hidden)>

Why is Joe signing off on these patches?  As his is the first sign-off, one
assumes that he was responsible for creating the patch in the first place,
but there is no From: line marking him as the author.  Shouldn't his entry
be an Acked-by: ?

Confused.

For this patch,
I just cherry-pick from Joe,
If you are not responsible for this part,
I will submit to the maintainers for these patches .
Sorry for that .