linux-kernel - Re: [PATCH] PCI/PM: Keep runtime PM enabled for unbound PCI devices

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Date:	Tue, 4 Dec 2012 17:06:36 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Huang Ying <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] PCI/PM: Keep runtime PM enabled for unbound PCI devices

On Wed, Nov 28, 2012 at 3:43 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, November 28, 2012 03:25:59 PM Bjorn Helgaas wrote:
>> On Tue, Nov 20, 2012 at 1:08 AM, Huang Ying <ying.huang@...el.com> wrote:
>> > For unbound PCI devices, what we need is:
>> >
>> >  - Always in D0 state, because some devices does not work again after
>> >    being put into D3 by the PCI bus.
>> >
>> >  - In SUSPENDED state if allowed, so that the parent devices can still
>> >    be put into low power state.
>> >
>> > To satisfy these requirement, the runtime PM for the unbound PCI
>> > devices are disabled and set to SUSPENDED state.  One issue of this
>> > solution is that the PCI devices will be put into SUSPENDED state even
>> > if the SUSPENDED state is forbidden via the sysfs interface
>> > (.../power/control) of the device.  This is not an issue for most
>> > devices, because most PCI devices are not used at all if unbounded.
>> > But there are exceptions.  For example, unbound VGA card can be used
>> > for display, but suspend its parents make it stop working.
>> >
>> > To fix the issue, we keep the runtime PM enabled when the PCI devices
>> > are unbound.  But the runtime PM callbacks will do nothing if the PCI
>> > devices are unbound.  This way, we can put the PCI devices into
>> > SUSPENDED state without put the PCI devices into D3 state.
>>
>> Does this fix a reported problem?  Is there a bug report URL?  What
>> problem would a user notice?
>
> There is a BZ: https://bugzilla.kernel.org/show_bug.cgi?id=48201

I added the BZ link and put this in my -next branch.  Thanks!

Bjorn
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