powerpc/papr_scm: Use ibm,unit-guid as the iset cookie

The interleave set cookie is used to determine if a label stored in the
metadata space should be applied to the current region. This is
important in the case of NVDIMMs since the firmware may change the
interleaving configuration of a DIMM which would invalidate the existing
labels. In our case the hypervisor hides those details from us so we
don't really care, but libnvdimm still requires the interleave set
cookie to be non-zero.

For our purposes we just need the set cookie to be unique and fixed for
a given PAPR SCM region and using the unit-guid (really a UUID) is fine
for this purpose.

Fixes: b5beae5e ("powerpc/pseries: Add driver for PAPR SCM regions")
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
[mpe: Use kernel types (u64)]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/papr_scm.c

@@ -264,6 +264,8 @@ static int papr_scm_probe(struct platform_device *pdev)
 	u32 drc_index, metadata_size;
 	u64 blocks, block_size;
 	struct papr_scm_priv *p;
+	const char *uuid_str;
+	u64 uuid[2];
 	int rc;
 
 	/* check we have all the required DT properties */
@@ -282,6 +284,11 @@ static int papr_scm_probe(struct platform_device *pdev)
 		return -ENODEV;
 	}
 
+	if (of_property_read_string(dn, "ibm,unit-guid", &uuid_str)) {
+		dev_err(&pdev->dev, "%pOF: missing unit-guid!\n", dn);
+		return -ENODEV;
+	}
+
 	p = kzalloc(sizeof(*p), GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
@@ -294,6 +301,11 @@ static int papr_scm_probe(struct platform_device *pdev)
 	p->block_size = block_size;
 	p->blocks = blocks;
 
+	/* We just need to ensure that set cookies are unique across */
+	uuid_parse(uuid_str, (uuid_t *) uuid);
+	p->nd_set.cookie1 = uuid[0];
+	p->nd_set.cookie2 = uuid[1];
+
 	/* might be zero */
 	p->metadata_size = metadata_size;
 	p->pdev = pdev;