[PATCH V5] PCI: loongson: Skip scanning unavailable child devices

[Liu Peibao]

The PCI Controller of 2K1000 could not mask devices by setting vender ID or
device ID in configuration space header as invalid values. When there are
pins shareable between the platform device and the on chip PCI device, if
the platform device is preferred, we should not scan this PCI device. In
the above scene, add `status = "disabled"` property in DT node of this PCI
device.

Before this patch, to solve the above problem, we treat the on chip PCI
devices as platform devices with fixed address assigned by the BIOS. When
there is device not preferred, add the `status = "disabled"` property in DT
node. In kernel, the PCI host bridge only scans slot 9/A/B/C/D/E that are
bridges. Overall, this looks not much elegant.

Signed-off-by: Liu Peibao <liupeibao@xxxxxxxxxxx>
---
V4 -> V5: make the issue we are facing clear 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