Re: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses

[Michael S. Tsirkin]

On Wed, Apr 29, 2020 at 06:28:46AM +0530, Ani Sinha wrote:
> Well there were several discussions in the other thread around how PCIE 
> behaves
> and how we can't change the slot features without a HW reset. Those were 
> useful
> inputs.

OK so I'd expect these to be addressed in some way. If we commit to
support a feature which has no chance to work on real hardware, we paint
ourselves into a tight corner. This kind of thing tends to create
maintainance problems down the road. Disabling both hotplug and unplug
sounds like a reasonable thing to do, so if there's a need to disable
just one of these, commit log needs to do a better job documenting the
usecase.

Alternatively, we need to be more creative with achieving what you are
trying to do in ways that can work on real hardware.

For example, how about hot-plugging a bridge which doesn't
support hotplug itself? Would that happen to make windows
do what you want, for both PCI and PCIE? We don't support
hotplugging bridges with devices behind them ATM, but
that sounds like a useful option.


Also, pcie root ports recently gained ability to disable hotplug, see
        commit 530a0963184e57e71a5b538e9161f115df533e96
        Author: Julia Suvorova <address@hidden>
        Date:   Wed Feb 26 18:46:07 2020 +0100

            pcie_root_port: Add hotplug disabling option

adding this to pci and pcie bridges sounds very reasonable.

-- 
MST