cxl/port: Introduce cxl_port_to_pci_bus()

Add a helper for converting a PCI enumerated cxl_port into the pci_bus
that hosts its dports. For switch ports this is trivial, but for root
ports there is no generic way to go from a platform defined host bridge
device, like ACPI0016 to its corresponding pci_bus. Rather than spill
ACPI goop outside of the cxl_acpi driver, just arrange for it to
register an xarray translation from the uport device to the
corresponding pci_bus.

This is in preparation for centralizing dport enumeration in the core.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
Link: https://lore.kernel.org/r/164364745633.85488.9744017377155103992.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index fc5d86222bc3..2a4230d685d5 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -25,6 +25,7 @@
  */
 
 static DEFINE_IDA(cxl_port_ida);
+static DEFINE_XARRAY(cxl_root_buses);
 
 static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
@@ -418,6 +419,42 @@ err:
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_add_port, CXL);
 
+struct pci_bus *cxl_port_to_pci_bus(struct cxl_port *port)
+{
+	/* There is no pci_bus associated with a CXL platform-root port */
+	if (is_cxl_root(port))
+		return NULL;
+
+	if (dev_is_pci(port->uport)) {
+		struct pci_dev *pdev = to_pci_dev(port->uport);
+
+		return pdev->subordinate;
+	}
+
+	return xa_load(&cxl_root_buses, (unsigned long)port->uport);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_port_to_pci_bus, CXL);
+
+static void unregister_pci_bus(void *uport)
+{
+	xa_erase(&cxl_root_buses, (unsigned long)uport);
+}
+
+int devm_cxl_register_pci_bus(struct device *host, struct device *uport,
+			      struct pci_bus *bus)
+{
+	int rc;
+
+	if (dev_is_pci(uport))
+		return -EINVAL;
+
+	rc = xa_insert(&cxl_root_buses, (unsigned long)uport, bus, GFP_KERNEL);
+	if (rc)
+		return rc;
+	return devm_add_action_or_reset(host, unregister_pci_bus, uport);
+}
+EXPORT_SYMBOL_NS_GPL(devm_cxl_register_pci_bus, CXL);
+
 static struct cxl_dport *find_dport(struct cxl_port *port, int id)
 {
 	struct cxl_dport *dport;