[PATCH v3 1/7] powerpc/pmem: Restrict papr_scm to P8 and above.

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

The PAPR based virtualized persistent memory devices are only supported on
POWER9 and above. In the followup patch, the kernel will switch the persistent
memory cache flush functions to use a new `dcbf` variant instruction. The new
instructions even though added in ISA 3.1 works even on P8 and P9 because these
are implemented as a variant of existing `dcbf` and `hwsync` and on P8 and
above behaves as such.

Considering these devices are only supported on P8 and above,  update the driver
to prevent a P7-compat guest from using persistent memory devices.

We don't update of_pmem driver with the same condition, because, on bare-metal,
the firmware enables pmem support only on P9 and above. There the kernel depends
on OPAL firmware to restrict exposing persistent memory related device tree
entries on older hardware. of_pmem.ko is written without any arch dependency and
we don't want to add ppc64 specific cpu feature check in of_pmem driver.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/pmem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/pmem.c b/arch/powerpc/platforms/pseries/pmem.c
index f860a897a9e0..2347e1038f58 100644
--- a/arch/powerpc/platforms/pseries/pmem.c
+++ b/arch/powerpc/platforms/pseries/pmem.c
@@ -147,6 +147,12 @@ const struct of_device_id drc_pmem_match[] = {
 
 static int pseries_pmem_init(void)
 {
+	/*
+	 * Only supported on POWER8 and above.
+	 */
+	if (!cpu_has_feature(CPU_FTR_ARCH_207S))
+		return 0;
+
 	pmem_node = of_find_node_by_type(NULL, "ibm,persistent-memory");
 	if (!pmem_node)
 		return 0;
-- 
2.26.2