powerpc32: memcpy: only use dcbz once cache is enabled

memcpy() uses instruction dcbz to speed up copy by not wasting time
loading cache line with data that will be overwritten.
Some platform like mpc52xx do no have cache active at startup and
can therefore not use memcpy(). Allthough no part of the code
explicitly uses memcpy(), GCC makes calls to it.

This patch modifies memcpy() such that at startup, memcpy()
unconditionally jumps to generic_memcpy() which doesn't use
the dcbz instruction.

Once the initial MMU is set up, in machine_init() we patch memcpy()
by replacing this inconditional jump by a NOP

Reported-by: Michal Sojka <sojkam1@fel.cvut.cz>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
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 bb02e9f6944e264f52e13d3f4cc1ea51beaccce2..b316ab787a3bcd8febe5e4aae15a3304dbbc586d 100644 (file)
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -38,6 +38,7 @@
 #include <asm/udbg.h>
 #include <asm/mmu_context.h>
 #include <asm/epapr_hcalls.h>
+#include <asm/code-patching.h>
 
 #define DBG(fmt...)
 
@@ -116,6 +117,8 @@ notrace void __init machine_init(u64 dt_ptr)
        /* Enable early debugging if any specified (see udbg.h) */
        udbg_early_init();
 
+       patch_instruction((unsigned int *)&memcpy, PPC_INST_NOP);
+
        /* 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 2ef50c6294709674ad69167b14ac8a5bede4631e..da5847d0971880f3e73833c8ded7e7646927149a 100644 (file)
--- a/arch/powerpc/lib/copy_32.S
+++ b/arch/powerpc/lib/copy_32.S
@@ -128,6 +128,10 @@ _GLOBAL(memset)
  * the destination area is cacheable.
  * We only use this version if the source and dest don't overlap.
  * -- paulus.
+ *
+ * During early init, cache might not be active yet, so dcbz cannot be used.
+ * We therefore jump to generic_memcpy which doesn't use dcbz. This jump is
+ * replaced by a nop once cache is active. This is done in machine_init()
  */
 _GLOBAL(memmove)
        cmplw   0,r3,r4
@@ -135,6 +139,7 @@ _GLOBAL(memmove)
        /* fall through */
 
 _GLOBAL(memcpy)
+       b       generic_memcpy
        add     r7,r3,r5                /* test if the src & dst overlap */
        add     r8,r4,r5
        cmplw   0,r4,r7