[Bug 271785] PCI: HotPlug: no BAR mapping after attaching a virtual function to the VM

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=271785

John Baldwin <jhb@FreeBSD.org> changed:

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--- Comment #2 from John Baldwin <jhb@FreeBSD.org> ---
I'm not quite sure I follow exactly.  Are you creating the VFs in a FreeBSD
bare metal machine, or have you created a VF on a host and are then passing
that VF through to the guest as a PCI-e hot-plug event?

Generally speaking, FreeBSD's PCI bus driver does not try to assign resources
to a device when it discovers it.  When a device is enumerated, if the BARs
already have a resource that has been assigned by firmware (e.g. during boot),
then this existing resource allocations are preserved and the address space is
reserved when enumerating the device.  However, if a BAR doesn't have a
firmware-assigned address range when a qdevice is enumerated, the BAR is still
sized but left unallocated.  If a device driver attaches and calls
bus_alloc_resource to reserve a BAR, at that point resources are allocated for
the BAR.

For HotPlug, BARs are always unassigned when the device appears, so they are
only assigned resources when you attach a driver.  Thus, if you create a VF on
the host and pass through to the FreeBSD guest and the guest doesn't have a
driver for the VF device loaded, I would expect to see all the BARs unassigned.
 However, once you load a driver the BARs should be assigned resources during
the attach of the device driver.

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