Re: [PATCH] PCI / hotplug: Propagate the "ignore hotplug" setting to parent

From: Bjorn Helgaas
Date: Wed Apr 15 2015 - 08:56:23 EST

On Tue, Apr 14, 2015 at 8:03 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Tuesday, April 14, 2015 12:28:12 PM Henrique de Moraes Holschuh wrote:
>> On Mon, Apr 13, 2015, at 11:23, Rafael J. Wysocki wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> >
>> > Refine the mechanism introduced by commit f244d8b623da (ACPIPHP / radeon
>> > / nouveau: Fix VGA switcheroo problem related to hotplug) to propagate
>> > the ignore_hotplug setting of the device to its parent bridge in case
>> > hotplug notifications related to the graphics adapter switching are
>> > given for the bridge rather than for the device itself (the need to
>> > be ignored in both cases).
>> I do apologise if this is a stupid question, but is there any chance the
>> bridge will be connected to other devices that do require hotplug handling,
>> and not just to the GPU?
> The bridge is actually a downstream PCIe port holding the GPU, so no. :-)

When radeon/nouveau call pci_ignore_hotplug(), that's the case, but in
general all we know is that pci_ignore_hotplug() receives a PCI
device. We don't know whether it's PCI or PCIe. In the hotplug
topologies I'm familiar with, a bridge only leads to one hot-pluggable
slot, but I don't remember anything that would guarantee that. For
PCIe, I think there can only be one slot, but for PCI I would think it
possible to have one bridge leading to several hotpluggable slots,
with the hotplug controller(s) being separate from the bridge.

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