pci_iov: Reuse downstream bridge bus window if it already covers VF bus

[chandrakanth.patil_broadcom.com]

Summary

If the parent bridge's [secondary, subordinate] window already covers
the VF bus (e.g., programmed by BIOS or a prior PF), skip allocating
PCI_RES_BUS. This avoids a duplicate rman allocation in the multi-PF
case while still allocating when growth is actually needed.

[jhb]

I need to think about this. I don't really want to have the PCI bus directly reading the config registers from the parent bridge. It's also true that you want to not release the bus until all VFs using that bus have been torn down, so you really kind of want a refcounted bus_alloc_resource here (in essence). It might be that just switching from RF_ACTIVE to RF_SHAREABLE when calling bus_alloc_resource is sufficient however.

[chandrakanth.patil_broadcom.com]

In D52163#1195416, @jhb wrote:

I need to think about this. I don't really want to have the PCI bus directly reading the config registers from the parent bridge. It's also true that you want to not release the bus until all VFs using that bus have been torn down, so you really kind of want a refcounted bus_alloc_resource here (in essence). It might be that just switching from RF_ACTIVE to RF_SHAREABLE when calling bus_alloc_resource is sufficient however.

ok. I tried with "RF_SHAREABLE" but still the "bus_alloc_resource" was returning NULL for VFs created on other PFs.

[chandrakanth.patil_broadcom.com]

Hi John,
I wanted to check if there are any updates on the suggestion I had asked.

[chandrakanth.patil_broadcom.com]

Hi John,

I am waiting for your inputs.