linux-kernel - Re: [Update][PATCH] PCI / PM: Disable runtime PM of PCIe ports

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Message-ID: <1676539.jiMCqtbGtq@vostro.rjw.lan>
Date:	Tue, 02 Apr 2013 01:20:27 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Martin Mokrejs <mmokrejs@...d.natur.cuni.cz>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Zheng Yan <zheng.z.yan@...el.com>
Subject: Re: [Update][PATCH] PCI / PM: Disable runtime PM of PCIe ports

On Monday, April 01, 2013 11:24:37 PM Rafael J. Wysocki wrote:
> On Monday, April 01, 2013 02:53:12 PM Bjorn Helgaas wrote:
> > On Mon, Apr 1, 2013 at 2:51 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > On Monday, April 01, 2013 11:34:46 AM Bjorn Helgaas wrote:
> > >> [+cc Zheng, who added this with 71a83bd727]
> > >>
> > >> On Sat, Mar 30, 2013 at 4:38 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > >> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > >> >
> > >> > The runtime PM of PCIe ports turns out to be quite fragile, as in
> > >> > some cases things work while in some other cases they don't and we
> > >> > don't seem to have a good way to determine whether or not they are
> > >> > going to work in advance.
> > >>
> > >> Do you have any references to problems encountered when enabling
> > >> runtime PM for PCIe ports?  That information will be useful to anybody
> > >> who wants to take another crack at getting this working.
> > >
> > > Well, bug 53811 is one example and problems recently reported by
> > > Martin are another.  Do you want me to dig deeper?
> > 
> > OK, I got this one:
> > 
> >   https://bugzilla.kernel.org/show_bug.cgi?id=53811
> > 
> > Martin has reported a lot of problems lately, and I don't know which
> > are related to runtime PM for PCIe ports.  I was hoping for a couple
> > URLs to put in the changelog so that when somebody gets the itch to
> > make this work, they have some useful info to start from.  If you
> > point me at a specific message, I'll dig up an archive URL for it.
> 
> This is the message in which Martin confirmed that the previous version of
> the $subject patch made insert/removal of devices into xHCI ports on his
> system work again.
> 
> > Otherwise, I'm afraid we'll just oscillate between "enable PM, find
> > bug, disable PM, enable PM, find same bug, disable PM, etc..."
> 
> That's a valid concern, but I think we have an idea about what kind of problems
> the runtime PM of PCIe ports may cause to happen (generally, PME and hotplug
> notifications may not work as expected).

I was thinking about this one in particular:

http://marc.info/?l=linux-acpi&m=136460903910718&w=2

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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