powerpc/32: remove a NOP from memset()

memset() is patched after initialisation to activate the
optimised part which uses cache instructions.

Today we have a 'b 2f' to skip the optimised patch, which then gets
replaced by a NOP, implying a useless cycle consumption.
As we have a 'bne 2f' just before, we could use that instruction
for the live patching, hence removing the need to have a
dedicated 'b 2f' to be replaced by a NOP.

This patch changes the 'bne 2f' by a 'b 2f'. During init, that
'b 2f' is then replaced by 'bne 2f'

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index 2f88f6c..51ebc01 100644 (file)
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -98,6 +98,9 @@ extern unsigned int memset_nocache_branch; /* Insn to be replaced by NOP */
 
 notrace void __init machine_init(u64 dt_ptr)
 {
+       unsigned int *addr = &memset_nocache_branch;
+       unsigned long insn;
+
        /* Configure static keys first, now that we're relocated. */
        setup_feature_keys();
 
@@ -105,7 +108,9 @@ notrace void __init machine_init(u64 dt_ptr)
        udbg_early_init();
 
        patch_instruction((unsigned int *)&memcpy, PPC_INST_NOP);
-       patch_instruction(&memset_nocache_branch, PPC_INST_NOP);
+
+       insn = create_cond_branch(addr, branch_target(addr), 0x820000);
+       patch_instruction(addr, insn);  /* replace b by bne cr0 */
 
        /* Do some early initialization based on the flat device tree */
        early_init_devtree(__va(dt_ptr));

diff --git a/arch/powerpc/lib/copy_32.S b/arch/powerpc/lib/copy_32.S
index 05aaee2..da425bb 100644 (file)
--- a/arch/powerpc/lib/copy_32.S
+++ b/arch/powerpc/lib/copy_32.S
@@ -103,9 +103,12 @@ _GLOBAL(memset)
        add     r5,r0,r5
        subf    r6,r0,r3
        cmplwi  0,r4,0
-       bne     2f      /* Use normal procedure if r4 is not zero */
+       /*
+        * Skip optimised bloc until cache is enabled. Will be replaced
+        * by 'bne' during boot to use normal procedure if r4 is not zero
+        */
 _GLOBAL(memset_nocache_branch)
-       b       2f      /* Skip optimised bloc until cache is enabled */
+       b       2f
 
        clrlwi  r7,r6,32-LG_CACHELINE_BYTES
        add     r8,r7,r5