[PATCH 2/2] powerpc/nvdimm: use H_SCM_QUERY hcall on H_OVERLAP error

[Aneesh Kumar K.V]

Right now we force an unbind of SCM memory at drcindex on H_OVERLAP error.
This really slows down operations like kexec where we get the H_OVERLAP
error because we don't go through a full hypervisor re init.

H_OVERLAP error for a H_SCM_BIND_MEM hcall indicates that SCM memory at
drc index is already bound. Since we don't specify a logical memory
address for bind hcall, we can use the H_SCM_QUERY hcall to query
the already bound logical address.

Boot time difference with and without patch is:

[    5.583617] IOMMU table initialized, virtual merging enabled
[    5.603041] papr_scm ibm,persistent-memory:ibm,pmemory at 44104001: Retrying bind after unbinding
[  301.514221] papr_scm ibm,persistent-memory:ibm,pmemory at 44108001: Retrying bind after unbinding
[  340.057238] hv-24x7: read 1530 catalog entries, created 537 event attrs (0 failures), 275 descs

after fix

[    5.101572] IOMMU table initialized, virtual merging enabled
[    5.116984] papr_scm ibm,persistent-memory:ibm,pmemory at 44104001: Querying SCM details
[    5.117223] papr_scm ibm,persistent-memory:ibm,pmemory at 44108001: Querying SCM details
[    5.120530] hv-24x7: read 1530 catalog entries, created 537 event attrs (0 failures), 275 descs

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
---
 arch/powerpc/platforms/pseries/papr_scm.c | 26 ++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
index 220e595cb579..4b74cfe7b334 100644
--- a/arch/powerpc/platforms/pseries/papr_scm.c
+++ b/arch/powerpc/platforms/pseries/papr_scm.c
@@ -110,6 +110,27 @@ static void drc_pmem_unbind(struct papr_scm_priv *p)
 	return;
 }
 
+static int drc_pmem_query(struct papr_scm_priv *p)
+{
+	unsigned long ret[PLPAR_HCALL_BUFSIZE];
+	int64_t rc;
+
+
+	rc = plpar_hcall(H_SCM_QUERY_BLOCK_MEM_BINDING, ret,
+			 p->drc_index, 0);
+
+	if (rc) {
+		dev_err(&p->pdev->dev, "Failed to bind SCM");
+		return rc;
+	}
+
+	p->bound_addr = ret[0];
+	dev_dbg(&p->pdev->dev, "bound drc 0x%x to %pR\n", p->drc_index, &p->res);
+
+	return 0;
+}
+
+
 static int papr_scm_meta_get(struct papr_scm_priv *p,
 			     struct nd_cmd_get_config_data_hdr *hdr)
 {
@@ -431,9 +452,8 @@ static int papr_scm_probe(struct platform_device *pdev)
 
 	/* If phyp says drc memory still bound then force unbound and retry */
 	if (rc == H_OVERLAP) {
-		dev_warn(&pdev->dev, "Retrying bind after unbinding\n");
-		drc_pmem_unbind(p);
-		rc = drc_pmem_bind(p);
+		dev_warn(&pdev->dev, "Querying SCM details\n");
+		rc = drc_pmem_query(p);
 	}
 
 	if (rc != H_SUCCESS) {
-- 
2.21.0