powerpc/32: Fix csum_partial_copy_generic()

Commit 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic()
based on copy_tofrom_user()") introduced a bug when destination
address is odd and initial csum is not null

In that (rare) case the initial csum value has to be rotated one byte
as well as the resulting value is

This patch also fixes related comments

Fixes: 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic() based on copy_tofrom_user()")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
index d90870a66b60b4b0820a3044466f70716e1ed610..0a57fe6d49ccf43a07224c4f7da1f597e36cc10c 100644 (file)
--- a/arch/powerpc/lib/checksum_32.S
+++ b/arch/powerpc/lib/checksum_32.S
@@ -127,8 +127,9 @@ _GLOBAL(csum_partial_copy_generic)
        stw     r7,12(r1)
        stw     r8,8(r1)
 
-       andi.   r0,r4,1                 /* is destination address even ? */
-       cmplwi  cr7,r0,0
+       rlwinm  r0,r4,3,0x8
+       rlwnm   r6,r6,r0,0,31   /* odd destination address: rotate one byte */
+       cmplwi  cr7,r0,0        /* is destination address even ? */
        addic   r12,r6,0
        addi    r6,r4,-4
        neg     r0,r4
@@ -237,7 +238,7 @@ _GLOBAL(csum_partial_copy_generic)
 66:    addze   r3,r12
        addi    r1,r1,16
        beqlr+  cr7
-       rlwinm  r3,r3,8,0,31    /* swap bytes for odd destination */
+       rlwinm  r3,r3,8,0,31    /* odd destination address: rotate one byte */
        blr
 
 /* read fault */