linux-kernel - Re: [PATCH 3/5] PCI: revert preparing for wakeup in runtime-suspend finalization

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Message-ID: <2547462.dZlJyWsOdA@vostro.rjw.lan>
Date:	Thu, 31 Jan 2013 02:13:58 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	e1000-devel@...ts.sourceforge.net, linux-pci@...r.kernel.org,
	Dave Airlie <airlied@...hat.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 3/5] PCI: revert preparing for wakeup in runtime-suspend finalization

On Tuesday, January 29, 2013 12:55:15 PM Rafael J. Wysocki wrote:
> On Tuesday, January 29, 2013 11:04:57 AM Konstantin Khlebnikov wrote:
> > Rafael J. Wysocki wrote:
> > > On Monday, January 28, 2013 04:17:42 PM Bjorn Helgaas wrote:
> > >> [+cc Rafael]
> > >>
> > >> On Fri, Jan 18, 2013 at 4:42 AM, Konstantin Khlebnikov
> > >> <khlebnikov@...nvz.org>  wrote:
> > >>> This patch effectively reverts commit 42eca2302146fed51335b95128e949ee6f54478f
> > >>> ("PCI: Don't touch card regs after runtime suspend D3")
> > >>>
> > >>> | This patch checks whether the pci state is saved and doesn't attempt to hit
> > >>> | any registers after that point if it is.
> > >>>
> > >>> This seems completely wrong. Yes, PCI configuration space has been saved by
> > >>> driver, but this doesn't means that all job is done and device has been
> > >>> suspended and ready for waking up in the future.
> > >>>
> > >>> For example driver e1000e for ethernet in my thinkpad x220 saves pci-state
> > >>> but device cannot wakeup after that, because it needs some ACPI callbacks
> > >>> which usually called from pci_finish_runtime_suspend().
> > >>>
> > >>> | Optimus (dual-gpu) laptops seem to have their own form of D3cold, but
> > >>> | unfortunately enter it on normal D3 transitions via the ACPI callback.
> > >>>
> > >>> Hardware which disappears from the bus unexpectedly is exception, so let's
> > >>> handle it as an exception. Its driver should set device state to D3cold and
> > >>> the rest code will handle it properly.
> > >>
> > >> Functions in D3cold don't have power, so it's completely expected that
> > >> they would disappear from the bus and not respond to config accesses.
> > >> Maybe Dave was referring to D3hot, where functions *should* respond to
> > >> config accesses.  I dunno.
> > >>
> > >> Just to be clear, it sounds like 42eca230 caused a regression on your
> > >> e1000e device?  If so, I guess we should revert it unless you and Dave
> > >> can figure out a better patch that fixes both your e1000e device and
> > >> the Optimus issue.
> > >
> > > Yes, if there's a regression, let's revert it, but I'd like the regression
> > > to be described clearly.
> > 
> > Yep, this is regression.
> > 
> > commit 42eca2302146fed51335b95128e949ee6f54478f ("PCI: Don't touch
> > card regs after runtime suspend D3") changes state convention during
> > runtime-suspend transaction too much. If PCI configuration space
> > has been saved by driver that does not means that all job is done
> > and device has been suspended and ready for waking up in the future.
> > 
> > e1000e saves pci-config space itself, but it requires operations which
> > pci_finish_runtime_suspend() does: preparing for wake (calling particular
> > platform pm-callbacks) and switching to proper sleep state.
> 
> Well, I'd argue this is a bug in e1000e.  Why does it need to save the PCI
> config space even though pci_pm_runtime_suspend() will do that anyway?

I honestly don't think we should revert 42eca2302146 because of this.

Yes, there is a requirement that drivers not save the PCI config space by
themselves unless they want to do the whole power management by themselves too
and e1000e is not following that.  So either we need to drop the
pci_save_state() from __e1000_shutdown() which I would prefer (I'm not really
sure why it is there), or e1000_runtime_suspend() needs to call
pci_finish_runtime_suspend() by itself.

Thanks,
Rafael


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