[PATCH V6] PCI: loongson: Skip scanning disabled child devices

[Liu Peibao]

Add a mechanism to disable on chip PCI devices by DT. Typically, when there
are pins shareable between the platform device and the on chip PCI device,
if the PCI device is not preferred, add `status = "disabled"` property to
this PCI device DT node.

For example, on LS2K1000, GMAC1 (on chip PCI device) and GPIO (platform
device, not PCI device) 14 share the same pin. If GMAC1 is not preferred,
add `status = "disabled"` property in GMAC1 DT node.

Signed-off-by: Liu Peibao <liupeibao@xxxxxxxxxxx>
---
V5 -> V6: 1. rewrite the commit log to make things clear.
	  2. replace "unavailable" as "disabled" in patch subject.
V4 -> V5: clear the issue we are facing in commit log.
V3 -> V4: 1. get rid of the masklist and search the status property
	  directly.
          2. check the status property only when accessing the vendor ID.
V2 -> V3: 1. use list_for_each_entry() for more clearly.
          2. fix wrong use of sizeof().
V1 -> V2: use existing property "status" instead of adding new property.

 drivers/pci/controller/pci-loongson.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
index 05c50408f13b..efca0b3b5a29 100644
--- a/drivers/pci/controller/pci-loongson.c
+++ b/drivers/pci/controller/pci-loongson.c
@@ -194,6 +194,17 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus,
 			return NULL;
 	}
 
+#ifdef CONFIG_OF
+	/* Don't access disabled devices. */
+	if (pci_is_root_bus(bus) && where == PCI_VENDOR_ID) {
+		struct device_node *dn;
+
+		dn = of_pci_find_child_device(bus->dev.of_node, devfn);
+		if (dn && !of_device_is_available(dn))
+			return NULL;
+	}
+#endif
+
 	/* CFG0 can only access standard space */
 	if (where < PCI_CFG_SPACE_SIZE && priv->cfg0_base)
 		return cfg0_map(priv, bus, devfn, where);
-- 
2.20.1