From: Will Deacon [mailto:will.deacon at arm.com]
Sent: Thursday, October 30, 2014 8:01 PM
To: Wang, Yalin
Cc: 'Rob Herring'; 'Joe Perches'; 'Russell King - ARM Linux'; 'linux-
kernel at vger.kernel.org'; 'akinobu.mita at gmail.com'; 'linux-mm at kvack.org';
'linux-arm-kernel at lists.infradead.org'
Subject: Re: [RFC V5 3/3] arm64:add bitrev.h file to support rbit
instruction

quoted

+static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
+{
+	if (__builtin_constant_p(x)) {
+		x = (x >> 16) | (x << 16);
+		x = ((x & 0xFF00FF00) >> 8) | ((x & 0x00FF00FF) << 8);
+		x = ((x & 0xF0F0F0F0) >> 4) | ((x & 0x0F0F0F0F) << 4);
+		x = ((x & 0xCCCCCCCC) >> 2) | ((x & 0x33333333) << 2);
+		return ((x & 0xAAAAAAAA) >> 1) | ((x & 0x55555555) << 1);

Shouldn't this part be in the generic code?

Good  idea, I will change this part into linux/bitrev.h .
Thanks