[Skiboot] [RFC PATCH] pci: Change bus number assignment policy

[Oliver]

On Tue, Mar 12, 2019 at 5:57 PM Oliver O'Halloran <oohall at gmail.com> wrote:
>
> Change the way we assign bus numbers so that rather than assigning
> bus numbers densely, we spread the available bus numbers across the
> downstream bridges of a given topology.
>
> For PCIe topologies with a wide-fan out this allows hot-plugging
> large numbers of devices into a downstream port near the top of the
> PCIe topology.
>
> This patch changes the bus number assignment policy to evenly split the
> available bus numbers across the bridges on bus. This allows us to
> support hot-adding of large numbers of devices near the root of the
> topology. Currently we only assign a handful of spare buses to each
> hotplug port so if a large number of devices are added at the root
> we won't have enough spare bus numbers for them.

I really should have proof-read that. Ah well.