Re: [PATCH v2] powerpc32: memcpy/memset: only use dcbz once cache is enabled

On Sat, 2015-09-12 at 11:57 +0200, christophe leroy wrote:

Le 11/09/2015 03:24, Michael Ellerman a écrit :

quoted

On Thu, 2015-09-10 at 17:05 -0500, Scott Wood wrote:

quoted

I don't think this duplication is what Michael meant by "the normal cpu
feature sections".  What else is going to use this very specific
infrastructure?

Yeah, sorry, I was hoping you could do it with the existing cpu feature
mechanism.

It looks like the timing doesn't work, ie. you need to patch this stuff in
machine_init(), which is later than the regular patching which gets done in
early_init().

This is one of the festering differences we have between the 32 and 64-bit
initialisation code, ie. on 64-bit we do the patching much later.

I've just thought about maybe another alternative.
Is there any issue with calling do_feature_fixups() twice for the same
features ?

Not that I can think of, but you never know.

If not, we could define a MMU_CACHE_NOW_ON dummy MMU feature, then
call again do_feature_fixups() in machine_init() to patch memcpy/memset 
stuff, something like:

In arch/powerpc/include/asm/mmu.h:
+#define MMU_CACHE_NOW_ON                ASM_CONST(0x00008000)

In arch/powerpc/kernel/setup_32.c: @machine_init()

         udbg_early_init();

+        spec = identify_cpu(0, mfspr(SPRN_PVR));
+        do_feature_fixups(spec->mmu_features | MMU_CACHE_NOW_ON,
+                          &__start___mmu_ftr_fixup,
+                          &__stop___mmu_ftr_fixup);

Did you try that? It would be cleaner, especially now that you have to do memset as well.

cheers