cxl/pmem: Introduce a find_cxl_root() helper

In preparation for switch port enumeration while also preserving the
potential for multi-domain / multi-root CXL topologies. Introduce a
'struct device' generic mechanism for retrieving a root CXL port, if one
is registered. Note that the only known multi-domain CXL configurations
are running the cxl_test unit test on a system that also publishes an
ACPI0017 device.

With this in hand the nvdimm-bridge lookup can be with
device_find_child() instead of bus_find_device() + custom mocked lookup
infrastructure in cxl_test.

The mechanism looks for a 2nd level port since the root level topology
is platform-firmware specific and the 2nd level down follows standard
PCIe topology expectations. The cxl_acpi 2nd level is associated with a
PCIe Root Port.

Reported-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/164367562182.225521.9488555616768096049.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
index 40b3f5030496..8de240c4d96b 100644
--- a/drivers/cxl/core/pmem.c
+++ b/drivers/cxl/core/pmem.c
@@ -57,24 +57,30 @@ bool is_cxl_nvdimm_bridge(struct device *dev)
 }
 EXPORT_SYMBOL_NS_GPL(is_cxl_nvdimm_bridge, CXL);
 
-__mock int match_nvdimm_bridge(struct device *dev, const void *data)
+static int match_nvdimm_bridge(struct device *dev, void *data)
 {
 	return is_cxl_nvdimm_bridge(dev);
 }
 
 struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_nvdimm *cxl_nvd)
 {
+	struct cxl_port *port = find_cxl_root(&cxl_nvd->dev);
 	struct device *dev;
 
-	dev = bus_find_device(&cxl_bus_type, NULL, cxl_nvd, match_nvdimm_bridge);
+	if (!port)
+		return NULL;
+
+	dev = device_find_child(&port->dev, NULL, match_nvdimm_bridge);
+	put_device(&port->dev);
+
 	if (!dev)
 		return NULL;
+
 	return to_cxl_nvdimm_bridge(dev);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_find_nvdimm_bridge, CXL);
 
-static struct cxl_nvdimm_bridge *
-cxl_nvdimm_bridge_alloc(struct cxl_port *port)
+static struct cxl_nvdimm_bridge *cxl_nvdimm_bridge_alloc(struct cxl_port *port)
 {
 	struct cxl_nvdimm_bridge *cxl_nvb;
 	struct device *dev;