nvdimm/pmem: Treat alloc_dax() -EOPNOTSUPP failure as non-fatal

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.

[ Based on commit "nvdimm/pmem: Fix leak on dax_add_host() failure". ]

Link: https://lkml.kernel.org/r/20240215144633.96437-4-mathieu.desnoyers@efficios.com
Fixes: d92576f1 ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Michael Sclafani <dm-devel@lists.linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/nvdimm/pmem.c

@@ -560,17 +560,19 @@ static int pmem_attach_disk(struct device *dev,
 	dax_dev = alloc_dax(pmem, &pmem_dax_ops);
 	if (IS_ERR(dax_dev)) {
 		rc = PTR_ERR(dax_dev);
-		goto out;
+		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;