device: Introduce pcidev_on_root() and friends

Semantics of dev_find_slot() are ill in the sense that
it only works after device enumeration has completed in
ramstage. Plan is to declare it as deprecated.

Introduce pcidev_on_root() and pcidev_path_on_root()
functions to replace cases where this was called with
static argument bus == 0. New implementation only walks
the root bus of the PCI tree, while old one walked
the entire linked list of devices.

Introduce pcidev_path_behind() to replace cases where
argument bus != 0. The required parent node is typically
one of the PCIe root functions that you locate using
pcidev_on_root() above.

New forms are safe to use with early devicetree and
before PCI bus numbers have been assigned.

Change-Id: Ie20598d48b4cf6e35e45fc90804bad4728437fc6
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/26447
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/include/device/device.h

@@ -276,6 +276,11 @@ DEVTREE_CONST struct device *dev_find_slot_pnp(u16 port, u16 device);
 DEVTREE_CONST struct device *dev_bus_each_child(const struct bus *parent,
 				DEVTREE_CONST struct device *prev_child);
 
+DEVTREE_CONST struct device *pcidev_path_behind(const struct bus *parent,
+		pci_devfn_t devfn);
+DEVTREE_CONST struct device *pcidev_path_on_root(pci_devfn_t devfn);
+DEVTREE_CONST struct device *pcidev_on_root(uint8_t dev, uint8_t fn);
+
 void scan_smbus(struct device *bus);
 void scan_generic_bus(struct device *bus);
 void scan_static_bus(struct device *bus);