linux-kernel - Re: [RFC PATCH] PCIe: Add PCIe runtime D3cold support

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Date:	Wed, 18 Apr 2012 22:51:46 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	huang ying <huang.ying.caritas@...il.com>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>, bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-pm@...r.kernel.org, Lin Ming <ming.m.lin@...el.com>,
	Zhang Rui <rui.zhang@...el.com>,
	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>
Subject: Re: [RFC PATCH] PCIe: Add PCIe runtime D3cold support

On Wednesday, April 18, 2012, huang ying wrote:
> On Wed, Apr 18, 2012 at 5:10 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Tuesday, April 17, 2012, huang ying wrote:
> >> On Tue, Apr 17, 2012 at 5:30 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> >> >> >> +     return 0;
> >> >> >> +}
> >> >> >> +
> >> >> >> +static int pcie_port_runtime_resume(struct device *dev)
> >> >> >> +{
> >> >> >> +     struct pci_dev *pdev = to_pci_dev(dev);
> >> >> >> +
> >> >> >> +     pci_restore_state(pdev);
> >> >> >> +     if (pdev->runtime_d3cold)
> >> >> >> +             msleep(100);
> >> >> >
> >> >> > What's _that_ supposed to do?
> >> >>
> >> >> When resume from d3cold, PCIe main link will be powered on again, it
> >> >> will take quite some time before the main link go into L0 state.
> >> >> Otherwise, accessing devices under the port may return wrong result.
> >> >
> >> > OK, but this is generic code and as per the standard the link should have been
> >> > reestablished at this point already.
> >> >
> >> > Please don't put some nonstandard-platform-specific quirks like this into
> >> > code that's supposed to handle _every_ PCIe system.
> >>
> >> After checking PCIe spec, I found that the 100ms here has its standard origin :)
> >>
> >> In PCI Express Base Specification Revision 2.0:
> >>
> >> Section 6.6.1 Conventional Reset
> >>
> >> "
> >> To allow components to perform internal initialization, system
> >> software must wait for at least
> >> 100 ms from the end of a Conventional Reset of one or more devices
> >> before it is permitted to
> >> issue Configuration Requests to those devices
> >> "
> >>
> >> But I think we should move the 100ms delay here to PCIe bus code or
> >> PCIe/ACPI code, because that is needed by all PCIe devices for D3cold
> >> support.
> >
> > I think it should be sufficient to wait for the PME message to arrive at
> > the root port (which will cause the PME interrupt to appear), at which
> > point the device that sent it should be able to receive configuration
> > requests.
> 
> For remote wake up, it is sufficient.  But for host wake up, we still
> need to wait 100ms.

Yes, we do.

> > At this point, I need to konw what exactly happens when the GPE is triggered
> > by WAKE#.
> 
> - Lxx handler will be executed
> - in Lxx handler, Notify the ACPI handle PCIe port
> - Linux has registered a handler for the ACPI handle of PCIe port, in
> the handler, turn on _PR0 and execute _PS0, which will power on the
> link.

But the handler we have is not the handler we want here.

In fact, there are two handlers, pci_acpi_wake_bus() and pci_acpi_wake_dev()
and they only do useful things for ACPI_NOTIFY_DEVICE_WAKE.  Is that the
event type we receive from that _Lxx?

Even if so, these routines don't seem to be suitable to handle the case at hand.

Thanks,
Rafael
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