[POWERPC] Use 1TB segments

This makes the kernel use 1TB segments for all kernel mappings and for
user addresses of 1TB and above, on machines which support them
(currently POWER5+, POWER6 and PA6T).

We detect that the machine supports 1TB segments by looking at the
ibm,processor-segment-sizes property in the device tree.

We don't currently use 1TB segments for user addresses < 1T, since
that would effectively prevent 32-bit processes from using huge pages
unless we also had a way to revert to using 256MB segments.  That
would be possible but would involve extra complications (such as
keeping track of which segment size was used when HPTEs were inserted)
and is not addressed here.

Parts of this patch were originally written by Ben Herrenschmidt.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/asm-powerpc/cputable.h b/include/asm-powerpc/cputable.h
index d913f460e710..ae093ef68363 100644
--- a/include/asm-powerpc/cputable.h
+++ b/include/asm-powerpc/cputable.h
@@ -164,6 +164,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTR_CELL_TB_BUG             LONG_ASM_CONST(0x0000800000000000)
 #define CPU_FTR_SPURR                   LONG_ASM_CONST(0x0001000000000000)
 #define CPU_FTR_DSCR                    LONG_ASM_CONST(0x0002000000000000)
+#define CPU_FTR_1T_SEGMENT              LONG_ASM_CONST(0x0004000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -374,7 +375,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTRS_POSSIBLE       \
             (CPU_FTRS_POWER3 | CPU_FTRS_RS64 | CPU_FTRS_POWER4 |        \
             CPU_FTRS_PPC970 | CPU_FTRS_POWER5 | CPU_FTRS_POWER6 |       \
-            CPU_FTRS_CELL | CPU_FTRS_PA6T)
+            CPU_FTRS_CELL | CPU_FTRS_PA6T | CPU_FTR_1T_SEGMENT)
 #else
 enum {
         CPU_FTRS_POSSIBLE =