[PATCH 13/15] cxl/acpi: Rework devm_cxl_enumerate_ports() to support RCD mode

[Robert Richter]

RCD mode has a different enumeration scheme other than in CXL VH mode.
An RCD is directly connected to an RCH without downstream and upstream
ports showing up in between in the PCI hierarchy. Due to the direct
connection of RCD and RCH, the host bridge is always the RCD's parent
instead of the grandparent. Modify devm_cxl_enumerate_ports()
respectively.

Implement this by introducing a function to determine the device's
downstream port. The 'for' loop is adjusted for RCD mode and in this
case find_cxl_port() will always find the host's associated port and
the loop iteration stops.

Signed-off-by: Robert Richter <rrichter@xxxxxxx>
---
 drivers/cxl/core/port.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 61e9915162d5..08b99423dbf8 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1084,6 +1084,22 @@ static struct device *grandparent(struct device *dev)
 	return NULL;
 }
 
+static struct device *cxl_mem_dport_dev(struct cxl_memdev *cxlmd)
+{
+	struct device *dev = cxlmd->dev.parent;
+	struct pci_dev *pdev = to_pci_dev(cxlmd->dev.parent);
+
+	/*
+	 * An RCiEP is directly connected to the root bridge without
+	 * any PCI bridges/ports in between. Reduce the parent level
+	 * for those.
+	 */
+	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_RC_END)
+		return dev;
+
+	return dev->parent;
+}
+
 static void delete_endpoint(void *data)
 {
 	struct cxl_memdev *cxlmd = data;
@@ -1339,7 +1355,7 @@ static int add_port_attach_ep(struct cxl_memdev *cxlmd,
 int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
 {
 	struct device *dev = &cxlmd->dev;
-	struct device *iter;
+	struct device *dport_dev;
 	int rc;
 
 	rc = devm_add_action_or_reset(&cxlmd->dev, cxl_detach_ep, cxlmd);
@@ -1352,25 +1368,21 @@ int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd)
 	 * attempt fails.
 	 */
 retry:
-	for (iter = dev; iter; iter = grandparent(iter)) {
-		struct device *dport_dev = grandparent(iter);
+	for (dport_dev = cxl_mem_dport_dev(cxlmd); dport_dev;
+	     dport_dev = grandparent(dport_dev)) {
 		struct device *uport_dev;
 		struct cxl_dport *dport;
 		struct cxl_port *port;
 
-		if (!dport_dev)
-			return 0;
-
 		uport_dev = dport_dev->parent;
 		if (!uport_dev) {
-			dev_warn(dev, "at %s no parent for dport: %s\n",
-				 dev_name(iter), dev_name(dport_dev));
+			dev_warn(dev, "no parent for dport: %s\n",
+				 dev_name(dport_dev));
 			return -ENXIO;
 		}
 
-		dev_dbg(dev, "scan: iter: %s dport_dev: %s parent: %s\n",
-			dev_name(iter), dev_name(dport_dev),
-			dev_name(uport_dev));
+		dev_dbg(dev, "scan: dport_dev: %s parent: %s\n",
+			dev_name(dport_dev), dev_name(uport_dev));
 		port = find_cxl_port(dport_dev, &dport);
 		if (port) {
 			dev_dbg(&cxlmd->dev,
@@ -1418,7 +1430,7 @@ EXPORT_SYMBOL_NS_GPL(devm_cxl_enumerate_ports, CXL);
 struct cxl_port *cxl_mem_find_port(struct cxl_memdev *cxlmd,
 				   struct cxl_dport **dport)
 {
-	return find_cxl_port(grandparent(&cxlmd->dev), dport);
+	return find_cxl_port(cxl_mem_dport_dev(cxlmd), dport);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_mem_find_port, CXL);
 
-- 
2.30.2