Re: [RFC PATCH] PCIe: Add PCIe runtime D3cold support

[huang ying]

On Tue, Apr 17, 2012 at 5:30 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
>> >> + Â Â return 0;
>> >> +}
>> >> +
>> >> +static int pcie_port_runtime_resume(struct device *dev)
>> >> +{
>> >> + Â Â struct pci_dev *pdev = to_pci_dev(dev);
>> >> +
>> >> + Â Â pci_restore_state(pdev);
>> >> + Â Â if (pdev->runtime_d3cold)
>> >> + Â Â Â Â Â Â 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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