Re: [PATCH v2] powerpc/mm: Add mask of always present MMU features

[Christophe Leroy]

Le 21/10/2020 à 16:25, Aneesh Kumar K.V a écrit :
Christophe Leroy <christophe.le...@csgroup.eu> writes:

Le 12/10/2020 à 17:39, Christophe Leroy a écrit :
On the same principle as commit 773edeadf672 ("powerpc/mm: Add mask
of possible MMU features"), add mask for MMU features that are
always there in order to optimise out dead branches.

Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
v2: Features must be anded with MMU_FTRS_POSSIBLE instead of ~0, otherwise
      MMU_FTRS_ALWAYS is ~0 when no #ifdef matches.

This is still not enough. For BOOK3S/32, MMU_FTRS_POSSIBLE is still too much.
We need a #ifdef CONFIG_PPC_BOOK3S_32 with 0.

Christophe

---
   arch/powerpc/include/asm/mmu.h | 25 +++++++++++++++++++++++++
   1 file changed, 25 insertions(+)

diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 255a1837e9f7..64e7e7f7cda9 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -201,8 +201,30 @@ enum {
                0,
   };
   
+enum {
+       MMU_FTRS_ALWAYS =
+#ifdef CONFIG_PPC_8xx
+               MMU_FTR_TYPE_8xx &
+#endif
+#ifdef CONFIG_40x
+               MMU_FTR_TYPE_40x &
+#endif
+#ifdef CONFIG_PPC_47x
+               MMU_FTR_TYPE_47x &
+#elif defined(CONFIG_44x)
+               MMU_FTR_TYPE_44x &
+#endif
+#if defined(CONFIG_E200) || defined(CONFIG_E500)
+               MMU_FTR_TYPE_FSL_E &
+#endif
+               MMU_FTRS_POSSIBLE,
+};

Will it be simpler if we make it a #define like below?

#ifdef CONFIG_PPC_8XX
#define MMU_FTR_ALWAYS  MMU_FTR_TYPE_8XX & MMU_FTR_POSSIBLE
#endif

Yes you are right, it will be simpler, and consistant with CPU_FTR_ALWAYS which is partly set with 
defines after all.

Christophe




+
   static inline bool early_mmu_has_feature(unsigned long feature)
   {
+       if (MMU_FTRS_ALWAYS & feature)
+               return true;
+
        return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
   }
   
@@ -231,6 +253,9 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
        }
   #endif
   
+	if (MMU_FTRS_ALWAYS & feature)
+               return true;
+
        if (!(MMU_FTRS_POSSIBLE & feature))
                return false;