path: root/arch
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authorAnton Blanchard <>2016-04-15 12:06:13 +1000
committerMichael Ellerman <>2016-04-18 20:08:38 +1000
commit6997e57d693b07289694239e52a10d2f02c3a46f (patch)
tree178b060e6aa7271a9bb7d8fde08d5bbf25d1e1b0 /arch
parent71528d8bd7a8aa920cd69d4223c6c87d5849257d (diff)
powerpc: scan_features() updates incorrect bits for REAL_LE
The REAL_LE feature entry in the ibm_pa_feature struct is missing an MMU feature value, meaning all the remaining elements initialise the wrong values. This means instead of checking for byte 5, bit 0, we check for byte 0, bit 0, and then we incorrectly set the CPU feature bit as well as MMU feature bit 1 and CPU user feature bits 0 and 2 (5). Checking byte 0 bit 0 (IBM numbering), means we're looking at the "Memory Management Unit (MMU)" feature - ie. does the CPU have an MMU. In practice that bit is set on all platforms which have the property. This means we set CPU_FTR_REAL_LE always. In practice that seems not to matter because all the modern cpus which have this property also implement REAL_LE, and we've never needed to disable it. We're also incorrectly setting MMU feature bit 1, which is: #define MMU_FTR_TYPE_8xx 0x00000002 Luckily the only place that looks for MMU_FTR_TYPE_8xx is in Book3E code, which can't run on the same cpus as scan_features(). So this also doesn't matter in practice. Finally in the CPU user feature mask, we're setting bits 0 and 2. Bit 2 is not currently used, and bit 0 is: #define PPC_FEATURE_PPC_LE 0x00000001 Which says the CPU supports the old style "PPC Little Endian" mode. Again this should be harmless in practice as no 64-bit CPUs implement that mode. Fix the code by adding the missing initialisation of the MMU feature. Also add a comment marking CPU user feature bit 2 (0x4) as reserved. It would be unsafe to start using it as old kernels incorrectly set it. Fixes: 44ae3ab3358e ("powerpc: Free up some CPU feature bits by moving out MMU-related features") Signed-off-by: Anton Blanchard <> Cc: [mpe: Flesh out changelog, add comment reserving 0x4] Signed-off-by: Michael Ellerman <>
Diffstat (limited to 'arch')
2 files changed, 2 insertions, 1 deletions
diff --git a/arch/powerpc/include/uapi/asm/cputable.h b/arch/powerpc/include/uapi/asm/cputable.h
index 8dde19962a5b..f63c96cd3608 100644
--- a/arch/powerpc/include/uapi/asm/cputable.h
+++ b/arch/powerpc/include/uapi/asm/cputable.h
@@ -31,6 +31,7 @@
+/* Reserved - do not use 0x00000004 */
#define PPC_FEATURE_TRUE_LE 0x00000002
#define PPC_FEATURE_PPC_LE 0x00000001
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 7030b035905d..080c96b44a7f 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -158,7 +158,7 @@ static struct ibm_pa_feature {
{CPU_FTR_NOEXECUTE, 0, 0, 0, 6, 0},
{CPU_FTR_NODSISRALIGN, 0, 0, 1, 1, 1},
{0, MMU_FTR_CI_LARGE_PAGE, 0, 1, 2, 0},
* If the kernel doesn't support TM (ie. CONFIG_PPC_TRANSACTIONAL_MEM=n),
* we don't want to turn on CPU_FTR_TM here, so we use CPU_FTR_TM_COMP