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

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Message-ID: <CAErSpo4tOqv+raFs2LH8sYBmg9vTbNAmKt2KSKFkCJ1dc_QJsw@mail.gmail.com>
Date:	Wed, 15 Apr 2015 07:55:26 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Linux PCI <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI / hotplug: Propagate the "ignore hotplug" setting to parent

On Tue, Apr 14, 2015 at 8:03 PM, Rafael J. Wysocki <rjw@...ysocki.net> 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@...el.com>
>> >
>> > 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.

Bjorn
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