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    SubjectRe: [PATCH v4] PCI: add kernel parameter to override devid<->driver mapping.
    Hi Marcel,

    I'm not quite clear on what the objective is here, so I apologize for
    some questions that probably seem silly.

    On Mon, Oct 20, 2014 at 8:04 AM, Marcel Apfelbaum <marcel.a@redhat.com> wrote:
    > Scanning a lot of devices during boot requires a lot of time.

    I think what takes a lot of time is the .probe() method for some
    drivers, right? I first thought you meant that it took a long time
    for the PCI core to enumerate a lot of devices, but you're not
    changing anything there.

    If the intent is to reduce boot time, I don't think this is a general
    solution. Drivers should be able to schedule asynchronous things in
    their .probe() methods if necessary.

    > On other scenarios there is a need to bind a driver to a specific slot.

    A short example here would be good. Are you talking about something
    like binding a NIC driver to one device while leaving others unbound
    for use by guests?

    > Binding devices to pci-stub driver does not work,
    > as it will not differentiate between devices of the
    > same type.

    I assume you mean booting with "pci-stub.ids=$VENDOR:$DEVICE" will
    make pci-stub bind to *all* matching devices, and you only want it to
    bind to some. Maybe pci-stub could be extended to pay attention to
    PCI bus addresses in addition to vendor/device IDs.

    > Using some start scripts is error prone.
    >
    > The solution leverages driver_override functionality introduced by
    >
    > commit: 782a985d7af26db39e86070d28f987cad21313c0
    > Author: Alex Williamson <alex.williamson@redhat.com>
    > Date: Tue May 20 08:53:21 2014 -0600
    >
    > PCI: Introduce new device binding path using pci_dev.driver_override
    >
    > In order to bind PCI slots to specific drivers use:
    > pci=driver[xxxx:xx:xx.x]=foo,driver[xxxx:xx:xx.x]=bar,...

    If/when you address Alex's comments about other bus types, can you
    also update the changelog to use the canonical commit reference
    format, i.e., 782a985d7af2 ("PCI: Introduce new device binding path
    using pci_dev.driver_override") in this case?

    PCI bus numbers are mutable, e.g., they can change with hotplug or
    other configuration changes. But I don't have any better suggestion,
    so I guess all we can do is be aware of this.

    Speaking of hotplug, this is only a boot-time kernel parameter, with
    no opportunity to use this, e.g., to add slot/driver pairs, after
    boot. Do you not need that because of Alex's driver_override thing?
    How can we integrate this all together into a coherent whole? I'm a
    little confused as to how this would all be documented in a form
    usable by end-users.

    Bjorn


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