Hello I'm writing a custom PCI driver for a hobby endpoint. Due to some "special", possibly unique, circumstance, I need to determine if two devices form a pair. As I'm using a PCI switch to connect these two devices, I'm thinking on the possibility of checking if the two devices share a common pci-pci bridge (or finding the least common ancestor in a directed graph). Basically, I'm trying to implement pci/bus.c::pci_walk_bus(), only, in a downstream direction (from end point to bridge). I could use pci_bus_upstream_bridge() to do my reverse walk but I noticed it uses a semaphore pci_bus_sem that is only made available via internal "pci.h" e.g. not available to outside modules. Along with my study, I would like to ask for advice and a push in the right direction on how can I achieve a reverse PCI walk - if that is possible. Thank you in advance for your help. ~amerei