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

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Date:	Fri, 20 Apr 2012 08:53:07 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 Thu, Apr 19, 2012 at 8:36 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Thursday, April 19, 2012, huang ying wrote:
>> On Thu, Apr 19, 2012 at 4:51 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> > 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?
>>
>> I check the DSDT, in _Lxx, there is
>>
>> Notify (\_SB.PCI0.RP03, 0x02)
>>
>> That is, the event type is ACPI_NOTIFY_DEVICE_WAKE.
>>
>> > Even if so, these routines don't seem to be suitable to handle the case at hand.
>>
>> Yes.  Maybe add a flag named like "come_from_d3cold", and if
>> come_from_d3cold == true, resume the dev itself without checking pme
>> bits, because the PCIe main link is not available now.
>
> Actually, I think we can do the full resume (however with the 100 ms wait)
> in that case, because we're going to resume the device shortly anyway.
>
> The PME would only be useful as a kind of handshake with the device, so we
> know we can access its registers, but as you pointed that out, we need the
> 100 ms delay in the host wakeup case anyway, so perhaps it's better to make
> remote wakeup and host wakeup behave identically in that respect.

Yes.

Best Regards,
Huang Ying
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