device: Add a helper to find device behind a PCI-to-PCI bridge device

This change adds a helper function to find PCI device with dev# and
function# behind a PCI-to-PCI bridge device.

BUG=b:153858769
BRANCH=None
TEST=None

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: Ie5672b35cda66431a0f1977f217bdf61d3012ace
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40474
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/device/device_const.c

@@ -232,6 +232,19 @@ DEVTREE_CONST struct device *pcidev_on_root(uint8_t dev, uint8_t fn)
 	return pcidev_path_on_root(PCI_DEVFN(dev, fn));
 }
 
+DEVTREE_CONST struct device *pcidev_path_behind_pci2pci_bridge(
+							const struct device *bridge,
+							pci_devfn_t devfn)
+{
+	if (!bridge || (bridge->path.type != DEVICE_PATH_PCI)) {
+		assert(0);
+		/* Return NULL in case asserts are non-fatal. */
+		return NULL;
+	}
+
+	return pcidev_path_behind(bridge->link_list, devfn);
+}
+
 DEVTREE_CONST struct device *pcidev_path_on_root_debug(pci_devfn_t devfn, const char *func)
 {
 	DEVTREE_CONST struct device *dev = pcidev_path_on_root(devfn);

src/include/device/device.h

@@ -293,6 +293,10 @@ DEVTREE_CONST struct device *pcidev_path_on_root(pci_devfn_t devfn);
 DEVTREE_CONST struct device *pcidev_path_on_bus(unsigned int bus, pci_devfn_t devfn);
 DEVTREE_CONST struct device *pcidev_on_root(uint8_t dev, uint8_t fn);
 DEVTREE_CONST struct bus *pci_root_bus(void);
+/* Find PCI device with given D#:F# sitting behind the given PCI-to-PCI bridge device. */
+DEVTREE_CONST struct device *pcidev_path_behind_pci2pci_bridge(
+							const struct device *bridge,
+							pci_devfn_t devfn);
 
 /* To be deprecated, avoid using.
  *