"Gleb O. Raiko" wrote: > > Jun Sun wrote: > > > You may control pci_scan_bridge by pcibios_assign_all_busses, just > > > return 0 from the latter and the code in pci_scan_bridge assigns all > > > numbers itself. > > > > Do you mean that we call pci_scan_brige first before scaning other devices? > > > > Yes I do. Look at drivers/pci/pci.c. The code does > > for each bus (by recursion) > scan devices on this bus > for each bridge on this bus > scan bridge > scan bus behind bridge > > The flow is pci_do_scan_bus -> pci_scan_bridge -> pci_do_scan_bus > > > > You definitely can't mix device discovering and assignment of resources > > > in one pass a on a multi-board cPCI system. > > > > > > > I have not given enough thought on 3), but it is certainly desirable. > > Well, your previous example works here. You perform scanning of devices > and assignments in one pass. You find new device unassigned by > firmware/another CPU in cPCI system, then you need find a room in a PCI > space. You can't do that, because you don't know yet what rooms > firmware/another CPU has allocated, so you don't know what rooms are > free. > You can if you throw away all the previous assignement done by BIOS, like pci_auto.c approach. > > Like I said before, this is the old style of doing things. There are many > > drawbacks in this approach. Among them, one is to require lots of knowledge > > about PCI and how the following hookup functions are called. Not every > > porting engineer is willing to dive into that. There are some other problems > > too. > > Sorry, your reason doesn't convince me. I believe, a porting engineer > must know hardware and operating system internals very well irrespective > of what his wishes are. > > Could you explain other problems, please ? I am not actively working on PCI right now. A couple of problems I remembered are related to the fixup mechnisms. If you rely on BIOS assignment, than you cannot do fixup on a per-PCI-device basis, then you have to do fixup based on per-device/BIOS-combo basis. I think a couple of days ago, there was a question about the restriction of PCI memory space being the same as CPU physical address space. Using pci_auto allows you to control the PCI memory region you use and deal with the restriction more easily. BTW, your objection seems to stem from the objection against pci_auto. But so far I have not seen any good reasons for not using pci_auto. Did I miss anything? If pci_auto does make porting easier, is there any good reason to go to a more difficult route? If you compare code size, PCI auto is much much smaller than the pci_assign_unassigned_resources(). I really don't understand what is the complain here. Jun
