Subject: [PATCH v4 4/8] libnvdimm/nvdimm/flush: Allow architecture to override the flush barrier

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Fri, 29 May 2020 10:58:16 +0530

Architectures like ppc64 provide persistent memory specific barriers
that will ensure that all stores for which the modifications are
written to persistent storage by preceding dcbfps and dcbstps
instructions have updated persistent storage before any data
access or data transfer caused by subsequent instructions is initiated.
This is in addition to the ordering done by wmb()

Update nvdimm core such that architecture can use barriers other than
wmb to ensure all previous writes are architecturally visible for
the platform buffer flush.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 drivers/md/dm-writecache.c   | 2 +-
 drivers/nvdimm/region_devs.c | 8 ++++----
 include/linux/libnvdimm.h    | 4 ++++
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 613c171b1b6d..904fdbf2b089 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -540,7 +540,7 @@ static void ssd_commit_superblock(struct dm_writecache *wc)
 static void writecache_commit_flushed(struct dm_writecache *wc, bool wait_for_ios)
 {
 	if (WC_MODE_PMEM(wc))
-		wmb();
+		arch_pmem_flush_barrier();
 	else
 		ssd_commit_flushed(wc, wait_for_ios);
 }
diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index ccbb5b43b8b2..88ea34a9c7fd 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1216,13 +1216,13 @@ int generic_nvdimm_flush(struct nd_region *nd_region)
 	idx = this_cpu_add_return(flush_idx, hash_32(current->pid + idx, 8));
 
 	/*
-	 * The first wmb() is needed to 'sfence' all previous writes
-	 * such that they are architecturally visible for the platform
-	 * buffer flush.  Note that we've already arranged for pmem
+	 * The first arch_pmem_flush_barrier() is needed to 'sfence' all
+	 * previous writes such that they are architecturally visible for
+	 * the platform buffer flush. Note that we've already arranged for pmem
 	 * writes to avoid the cache via memcpy_flushcache().  The final
 	 * wmb() ensures ordering for the NVDIMM flush write.
 	 */
-	wmb();
+	arch_pmem_flush_barrier();
 	for (i = 0; i < nd_region->ndr_mappings; i++)
 		if (ndrd_get_flush_wpq(ndrd, i, 0))
 			writeq(1, ndrd_get_flush_wpq(ndrd, i, idx));
diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
index 18da4059be09..66f6c65bd789 100644
--- a/include/linux/libnvdimm.h
+++ b/include/linux/libnvdimm.h
@@ -286,4 +286,8 @@ static inline void arch_invalidate_pmem(void *addr, size_t size)
 }
 #endif
 
+#ifndef arch_pmem_flush_barrier
+#define arch_pmem_flush_barrier() wmb()
+#endif
+
 #endif /* __LIBNVDIMM_H__ */
-- 
2.26.2