[RFC PATCH v4 02/12] nvdimm/pmem: Treat alloc_dax() -EOPNOTSUPP failure as non-fatal

[Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>]

In preparation for checking whether the architecture has data cache
aliasing within alloc_dax(), modify the error handling of nvdimm/pmem
pmem_attach_disk() to treat alloc_dax() -EOPNOTSUPP failure as non-fatal.

For the transition, consider that alloc_dax() returning NULL is the
same as returning -EOPNOTSUPP.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Alasdair Kergon <agk@xxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: linux-cxl@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-xfs@xxxxxxxxxxxxxxx
Cc: dm-devel@xxxxxxxxxxxxxxx
Cc: nvdimm@xxxxxxxxxxxxxxx
---
 drivers/nvdimm/pmem.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 9fe358090720..f1d9f5c6dbac 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -558,19 +558,21 @@ static int pmem_attach_disk(struct device *dev,
 	disk->bb = &pmem->bb;
 
 	dax_dev = alloc_dax(pmem, &pmem_dax_ops);
-	if (IS_ERR(dax_dev)) {
-		rc = PTR_ERR(dax_dev);
-		goto out;
+	if (IS_ERR_OR_NULL(dax_dev)) {
+		rc = IS_ERR(dax_dev) ? PTR_ERR(dax_dev) : -EOPNOTSUPP;
+		if (rc != -EOPNOTSUPP)
+			goto out;
+	} else {
+		set_dax_nocache(dax_dev);
+		set_dax_nomc(dax_dev);
+		if (is_nvdimm_sync(nd_region))
+			set_dax_synchronous(dax_dev);
+		pmem->dax_dev = dax_dev;
+		rc = dax_add_host(dax_dev, disk);
+		if (rc)
+			goto out_cleanup_dax;
+		dax_write_cache(dax_dev, nvdimm_has_cache(nd_region));
 	}
-	set_dax_nocache(dax_dev);
-	set_dax_nomc(dax_dev);
-	if (is_nvdimm_sync(nd_region))
-		set_dax_synchronous(dax_dev);
-	pmem->dax_dev = dax_dev;
-	rc = dax_add_host(dax_dev, disk);
-	if (rc)
-		goto out_cleanup_dax;
-	dax_write_cache(dax_dev, nvdimm_has_cache(nd_region));
 	rc = device_add_disk(dev, disk, pmem_attribute_groups);
 	if (rc)
 		goto out_remove_host;
-- 
2.39.2