PCI: endpoint: Assign PCI domain number for endpoint controllers

Right now, PCI endpoint subsystem doesn't assign PCI domain number for the
PCI endpoint controllers. But this domain number could be useful to the EPC
drivers to uniquely identify each controller based on the hardware instance
when there are multiple ones present in an SoC (even multiple RC/EP).

So let's make use of the existing pci_bus_find_domain_nr() API to allocate
domain numbers based on either devicetree (linux,pci-domain) property or
dynamic domain number allocation scheme.

It should be noted that the domain number allocated by this API will be
based on both RC and EP controllers in a SoC. If the 'linux,pci-domain' DT
property is present, then the domain number represents the actual hardware
instance of the PCI endpoint controller. If not, then the domain number
will be allocated based on the PCI EP/RC controller probe order.

If the architecture doesn't support CONFIG_PCI_DOMAINS_GENERIC (rare), then
currently a warning is thrown to indicate that the architecture specific
implementation is needed.

Link: https://lore.kernel.org/linux-pci/20240828-pci-qcom-hotplug-v4-5-263a385fbbcb@linaro.orgSigned-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>

drivers/pci/endpoint/pci-epc-core.c

@@ -838,6 +838,10 @@ void pci_epc_destroy(struct pci_epc *epc)
 {
 	pci_ep_cfs_remove_epc_group(epc->group);
 	device_unregister(&epc->dev);
+
+#ifdef CONFIG_PCI_DOMAINS_GENERIC
+	pci_bus_release_domain_nr(NULL, &epc->dev);
+#endif
 }
 EXPORT_SYMBOL_GPL(pci_epc_destroy);
 
@@ -900,6 +904,16 @@ __pci_epc_create(struct device *dev, const struct pci_epc_ops *ops,
 	epc->dev.release = pci_epc_release;
 	epc->ops = ops;
 
+#ifdef CONFIG_PCI_DOMAINS_GENERIC
+	epc->domain_nr = pci_bus_find_domain_nr(NULL, dev);
+#else
+	/*
+	 * TODO: If the architecture doesn't support generic PCI
+	 * domains, then a custom implementation has to be used.
+	 */
+	WARN_ONCE(1, "This architecture doesn't support generic PCI domains\n");
+#endif
+
 	ret = dev_set_name(&epc->dev, "%s", dev_name(dev));
 	if (ret)
 		goto put_dev;

include/linux/pci-epc.h

@@ -128,6 +128,7 @@ struct pci_epc_mem {
  * @group: configfs group representing the PCI EPC device
  * @lock: mutex to protect pci_epc ops
  * @function_num_map: bitmap to manage physical function number
+ * @domain_nr: PCI domain number of the endpoint controller
  * @init_complete: flag to indicate whether the EPC initialization is complete
  *                 or not
  */
@@ -145,6 +146,7 @@ struct pci_epc {
 	/* mutex to protect against concurrent access of EP controller */
 	struct mutex			lock;
 	unsigned long			function_num_map;
+	int				domain_nr;
 	bool				init_complete;
 };