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    SubjectRe: [PATCH 2.6.26] PCI: refuse to re-add a device to a bus upon pci_scan_child_bus()

    You seem to have a finer grasp of the subject then I do, please correct/educate me on any of the points I raise in the following lines.

    Matthew Wilcox wrote:

    > On Tue, Jul 22, 2008 at 11:21:06AM +0300, eran liberty wrote:
    >>> I think this is your real problem, that you're rescanning the entire
    >>> bus. I don't think that's the route we'd recommend taking.
    >> My stating point was that I have loaded a new design into a
    >> programmable device which sits on the pci device. The new design can
    >> implement numerous pci devices or non at all. I can think of an easy
    >> way (or clean one) to scan only the programmable device. Scanning the
    >> whole bus seemed reasonable.
    > That's what pci_scan_slot() is for. It scans the first function at the
    > device number, then (if the header indicates it's a multifunction
    > device) scans the other functions associated with that device. eg you
    > could call pci_scan_slot(bus, 0x30) and it will create function 06.0
    > (and potentially 06.1, 06.2, ...)
    > You presumably already have the devfn for the existing device since
    > you're able to call pci_remove_bus_device().
    Each slot represent a single device which can have more then one function. pci_scan_slot is aimed for scanning these multiple functions.
    I, on the other hand, have programmable device on the pci bus which is, for the sake of this discussion, a complete black box.
    This black box up on loading can implement more then one device, which can have more then one function each.
    So as far as I see it, now I need to scan all slots on the bus.

    But to be honest, upon looking a way to make my device work I dismissed the "pci_scan_slot()" option as It did not reach the "fixup_resource <http://liberty/lxr/ident?v=e500-linux-2.6.26-rc4;i=fixup_resource>()" part.

    >>> Why don't you call pci_scan_slot() instead? You won't get the benefit of
    >>> pcibios_fixup_bus(), but I'm not convinced that's safe to call on a bus
    >>> that's already been scanned.
    >> As said its not exactly a slot its more like a regular pci device that
    >> someone suddenly welded into the pci bus. Its not a hotplug as well,
    >> and I do not want to give up on the pcibios_fixup_bus()
    > Why not? What architecture are you using? What does
    > pcibios_fixup_bus() do for you?
    I work with ARCH=powerpc. pcibios_fixup_bus() will deal with all the resource bars allocation.
    I needed Linux to renegotiate the resources bars on the PCI devices.

    > (as a side-note, I'd like to reimplement the pcibios_fixup_*() routines;
    > I think a lot of what they do can be done more generically these days.
    > It'll take a while and isn't high on my priority list).
    If I can lend a hand there, let me know and I will try to squeeze it in somewhere.

    >> As it is, with my patch applied i successfully go over the bus and
    >> remove my own devices before I reprogram the
    >> programmable device.
    >> while ((dev = pci_get_device(PCI_VENDOR_ID_MYCOMP,PCI_DEVICE_ID_MYDEV,NULL))
    >> != NULL) {
    >> pci_remove_bus_device(dev);
    >> pci_dev_put(dev);
    >> }
    >> Load a new design into it.
    >> Then scan the entire bus and add the newly discovered devices.
    >> bus = null;
    >> while ((bus = pci_find_next_bus(bus)) != NULL) {
    >> pci_scan_child_bus(bus);
    >> pci_bus_assign_resources(bus);
    >> pci_bus_add_devices(bus);
    >> }
    >> As seen here, this sequence of instructions seems very intuitive. It
    >> will fail without the patch upon pci_bus_add_devices().
    > Seems utterly unintuitive to me. You're doing a lot of unnecessary work
    > here, and if you have two cards in your machine, you'll take away both
    > of them when you reload either of them.
    Hmmm, I do want to remove all the devices that are implemented by the programmable unit which is reloaded.
    I have not considered the possibility of having more then one programmable unit.
    I guess that the removing part can be more fine tuned as the need arises.

    > What you should do is cache the pci_bus and the devfn at startup:
    > static struct pci_bus *my_bus;
    > static int my_devfn;
    > struct pci_dev *dev = pci_get_device(PCI_VENDOR_ID_MYCOMP,
    > if (!dev)
    > return -ENODEV;
    > my_bus = dev->bus;
    > my_devfn = dev->devfn;
    > pci_dev_put(dev);
    > when you want to remove it:
    > for (func = 0; func < 8; func++)
    > struct pci_dev *dev = pci_get_slot(my_bus, my_devfn + func);
    > if (!dev)
    > continue;
    > pci_remove_bus_device(dev);
    > pci_dev_put(dev);
    > }
    > when you want to rescan it:
    > pci_scan_slot(my_bus, my_devfn);
    > (this only handles one programmable card. The basic idea could be
    > extended to handle multiple cards if you need to do that).
    I think there is a hidden assumption in this code, again please correct me if I missed the point.
    This code assumes that the devices which will re-appear after the programmable unit is loaded has the same devfn and bus as the devices which were present before the reload.
    This assumption might be wrong.

    For example, I have a basic programmable image which has no pci devices at all.
    upon unloading I do not remove any device (as non are present) and up on reloading I suddenly have two. What is their bus? their devfn?

    Ultimately I would have expected to find a "int pci_scan_bus(struct <http://liberty/lxr/ident?v=e500-linux-2.6.26-rc4;i=pci_scan_bus>pci_bus <http://liberty/lxr/ident?v=e500-linux-2.6.26-rc4;i=pci_bus> *bus <http://liberty/lxr/ident?v=e500-linux-2.6.26-rc4;i=bus>);" the "pci_scan_child_bus <http://liberty/lxr/ident?v=e500-linux-2.6.26-rc4;i=pci_scan_child_bus>()" was the closest to the mark


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