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

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Date:	Tue, 17 Apr 2012 13:13:39 +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 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.

Best Regards,
Huang Ying
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