Date:	Sat, 02 Feb 2013 21:58:45 +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>
Subject: Re: [PATCH 3/5] PCI: revert preparing for wakeup in runtime-suspend finalization

On Saturday, February 02, 2013 04:12:03 PM Konstantin Khlebnikov wrote:
> Rafael J. Wysocki wrote:
> > 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.
> 
> Yet another problem: some drivers calls pci_save_state() from ->probe() callback
> to use this saved state in pci_error_handlers->slot_reset().
> As result pdev->state_saved is true mostly all time.
> At least e1000e and drivers/pci/pcie/portdrv_pci.c are doing this.
> 
> I think it will be safer to revert 42eca2302146 in v3.8

Well, I wonder if we can just do something like the appended patch instead and
address the e1000e runtime suspend by calling pci_finish_runtime_suspend()
directly from e1000_runtime_suspend().

While we can revert commit 42eca2302146, that hardly would be progress,
because then the issue it was supposed to address would still need to be
addressed somehow.

Thanks,
Rafael


---
 drivers/pci/pci-driver.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-pm/drivers/pci/pci-driver.c
===================================================================
--- linux-pm.orig/drivers/pci/pci-driver.c
+++ linux-pm/drivers/pci/pci-driver.c
@@ -628,6 +628,7 @@ static int pci_pm_suspend(struct device
 		goto Fixup;
 	}
 
+	pci_dev->state_saved = false;
 	if (pm->suspend) {
 		pci_power_t prev = pci_dev->current_state;
 		int error;
@@ -774,6 +775,7 @@ static int pci_pm_freeze(struct device *
 		return 0;
 	}
 
+	pci_dev->state_saved = false;
 	if (pm->freeze) {
 		int error;
 
@@ -862,6 +864,7 @@ static int pci_pm_poweroff(struct device
 		goto Fixup;
 	}
 
+	pci_dev->state_saved = false;
 	if (pm->poweroff) {
 		int error;
 
@@ -987,6 +990,7 @@ static int pci_pm_runtime_suspend(struct
 	if (!pm || !pm->runtime_suspend)
 		return -ENOSYS;
 
+	pci_dev->state_saved = false;
 	pci_dev->no_d3cold = false;
 	error = pm->runtime_suspend(dev);
 	suspend_report_result(pm->runtime_suspend, error);

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists