powerpc/mm: Add mask of possible MMU features

Follow the example of the cpu feature code, and add a mask of possible
MMU features, MMU_FTRS_POSSIBLE.

This is used in mmu_has_feature(), which allows the possible mask to act
as a shortcut for any features that are not possible, but still allows
the feature bit itself to be defined.

We will use this in the next commit to allow MMU_FTR_RADIX checks to be
elided when MMU_FTR_RADIX is not possible.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu.h

@@ -110,9 +110,21 @@
 DECLARE_PER_CPU(int, next_tlbcam_idx);
 #endif
 
+enum {
+	MMU_FTRS_POSSIBLE = MMU_FTR_HPTE_TABLE | MMU_FTR_TYPE_8xx |
+		MMU_FTR_TYPE_40x | MMU_FTR_TYPE_44x | MMU_FTR_TYPE_FSL_E |
+		MMU_FTR_TYPE_47x | MMU_FTR_USE_HIGH_BATS | MMU_FTR_BIG_PHYS |
+		MMU_FTR_USE_TLBIVAX_BCAST | MMU_FTR_USE_TLBILX |
+		MMU_FTR_LOCK_BCAST_INVAL | MMU_FTR_NEED_DTLB_SW_LRU |
+		MMU_FTR_USE_TLBRSRV | MMU_FTR_USE_PAIRED_MAS |
+		MMU_FTR_NO_SLBIE_B | MMU_FTR_16M_PAGE | MMU_FTR_TLBIEL |
+		MMU_FTR_LOCKLESS_TLBIE | MMU_FTR_CI_LARGE_PAGE |
+		MMU_FTR_1T_SEGMENT,
+};
+
 static inline int mmu_has_feature(unsigned long feature)
 {
-	return (cur_cpu_spec->mmu_features & feature);
+	return (MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
 }
 
 static inline void mmu_clear_feature(unsigned long feature)