Dan Williams [off-list ref] writes:

On Mon, Jun 29, 2020 at 6:58 AM Aneesh Kumar K.V
[off-list ref] wrote:

quoted

We only support persistent memory on P8 and above. This is enforced by the
firmware and further checked on virtualzied platform during platform init.
Add WARN_ONCE in pmem flush routines to catch the wrong usage of these.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/include/asm/cacheflush.h | 2 ++
 arch/powerpc/lib/pmem.c               | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/arch/powerpc/include/asm/cacheflush.h b/arch/powerpc/include/asm/cacheflush.h
index 95782f77d768..1ab0fa660497 100644
--- a/arch/powerpc/include/asm/cacheflush.h
+++ b/arch/powerpc/include/asm/cacheflush.h

@@ -103,6 +103,8 @@ static inline void  arch_pmem_flush_barrier(void)
 {
        if (cpu_has_feature(CPU_FTR_ARCH_207S))
                asm volatile(PPC_PHWSYNC ::: "memory");
+       else
+               WARN_ONCE(1, "Using pmem flush on older hardware.");

This seems too late to be making this determination. I'd expect the
driver to fail to successfully bind default if this constraint is not
met.

We do that in Patch 1.

-aneesh