[PATCH v2 5/5] powerpc/pmem: Avoid the barrier in flush routines

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

nvdimm expect the flush routines to just mark the cache clean. The barrier
that mark the store globally visible is done in nvdimm_flush().

Update the papr_scm driver to a simplified nvdim_flush callback that do
only the required barrier.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 arch/powerpc/lib/pmem.c                   | 34 +++++++++++++++++------
 arch/powerpc/platforms/pseries/papr_scm.c | 13 +++++++++
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/lib/pmem.c b/arch/powerpc/lib/pmem.c
index 076d75efb57a..3ef15cfa925b 100644
--- a/arch/powerpc/lib/pmem.c
+++ b/arch/powerpc/lib/pmem.c
@@ -9,7 +9,7 @@
 
 #include <asm/cacheflush.h>
 
-static inline void clean_pmem_range_isa310(unsigned long start, unsigned long stop)
+static inline void __clean_pmem_range(unsigned long start, unsigned long stop)
 {
 	unsigned long shift = l1_dcache_shift();
 	unsigned long bytes = l1_dcache_bytes();
@@ -18,13 +18,22 @@ static inline void clean_pmem_range_isa310(unsigned long start, unsigned long st
 	unsigned long i;
 
 	for (i = 0; i < size >> shift; i++, addr += bytes)
-		asm volatile(PPC_DCBSTPS(%0, %1): :"i"(0), "r"(addr): "memory");
+		dcbf(addr);
+}
 
+static inline void __flush_pmem_range(unsigned long start, unsigned long stop)
+{
+	unsigned long shift = l1_dcache_shift();
+	unsigned long bytes = l1_dcache_bytes();
+	void *addr = (void *)(start & ~(bytes - 1));
+	unsigned long size = stop - (unsigned long)addr + (bytes - 1);
+	unsigned long i;
 
-	asm volatile(PPC_PHWSYNC ::: "memory");
+	for (i = 0; i < size >> shift; i++, addr += bytes)
+		dcbf(addr);
 }
 
-static inline void flush_pmem_range_isa310(unsigned long start, unsigned long stop)
+static inline void clean_pmem_range_isa310(unsigned long start, unsigned long stop)
 {
 	unsigned long shift = l1_dcache_shift();
 	unsigned long bytes = l1_dcache_bytes();
@@ -33,24 +42,33 @@ static inline void flush_pmem_range_isa310(unsigned long start, unsigned long st
 	unsigned long i;
 
 	for (i = 0; i < size >> shift; i++, addr += bytes)
-		asm volatile(PPC_DCBFPS(%0, %1): :"i"(0), "r"(addr): "memory");
+		asm volatile(PPC_DCBSTPS(%0, %1): :"i"(0), "r"(addr): "memory");
+}
 
+static inline void flush_pmem_range_isa310(unsigned long start, unsigned long stop)
+{
+	unsigned long shift = l1_dcache_shift();
+	unsigned long bytes = l1_dcache_bytes();
+	void *addr = (void *)(start & ~(bytes - 1));
+	unsigned long size = stop - (unsigned long)addr + (bytes - 1);
+	unsigned long i;
 
-	asm volatile(PPC_PHWSYNC ::: "memory");
+	for (i = 0; i < size >> shift; i++, addr += bytes)
+		asm volatile(PPC_DCBFPS(%0, %1): :"i"(0), "r"(addr): "memory");
 }
 
 static inline void clean_pmem_range(unsigned long start, unsigned long stop)
 {
 	if (cpu_has_feature(CPU_FTR_ARCH_31))
 		return clean_pmem_range_isa310(start, stop);
-	return flush_dcache_range(start, stop);
+	return __clean_pmem_range(start, stop);
 }
 
 static inline void flush_pmem_range(unsigned long start, unsigned long stop)
 {
 	if (cpu_has_feature(CPU_FTR_ARCH_31))
 		return flush_pmem_range_isa310(start, stop);
-	return flush_dcache_range(start, stop);
+	return __flush_pmem_range(start, stop);
 }
 
 /*
diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index f35592423380..ad506e7003c9 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -285,6 +285,18 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
 
 	return 0;
 }
+/*
+ * We have made sure the pmem writes are done such that before calling this
+ * all the caches are flushed/clean. We use dcbf/dcbfps to ensure this. Here
+ * we just need to add the necessary barrier to make sure the above flushes
+ * are have updated persistent storage before any data access or data transfer
+ * caused by subsequent instructions is initiated.
+ */
+static int papr_scm_flush_sync(struct nd_region *nd_region, struct bio *bio)
+{
+	arch_pmem_flush_barrier();
+	return 0;
+}
 
 static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
 {
@@ -340,6 +352,7 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
 	ndr_desc.mapping = &mapping;
 	ndr_desc.num_mappings = 1;
 	ndr_desc.nd_set = &p->nd_set;
+	ndr_desc.flush = papr_scm_flush_sync;
 
 	if (p->is_volatile)
 		p->region = nvdimm_volatile_region_create(p->bus, &ndr_desc);
-- 
2.26.2