Re: Shutting down PCI devices on suspend

[Arjen Verweij <a.verweij-oe7qfRrRQfeEZXFvZSAUrfP6llvjuJOh@public.gmane.org>]

It would be swell if this worked for S5 as well. It's also the simplest 
case, since the hardware is reinitialised at boottime anyway.

Nate Lawson wrote:

> Matthew Garrett wrote:
>
>> On Sat, 2004-12-11 at 11:50 -0800, Nate Lawson wrote:
>>
>>> In FreeBSD, we do this at the bus layer.  So the ACPI and PCI bus 
>>> code is responsible for powering down/up children.  We currently do it:
>>>
>>> 1. When no driver is attached and on reprobe
>>> 2. When suspending/resuming, based on evaluating _SxD
>>>
>>> See this commit for details:
>>> http://docs.freebsd.org/cgi/getmsg.cgi?fetch=1604853+0+archive/2004/cvs-all/20041205.cvs-all 
>>>
>>
>>
>>
>> Does _SxD represent the "desired" mode for the hardware, or merely the
>> highest state it can be left in? A mail from Len earlier this year
>> suggested that if S3D returned 0x2, that meant that either D3 or D2 were
>> acceptable.
>
>
> _SxD is the highest state supported by the device for a given sleep 
> state, yes.  We put devices in D3 unless _SxD specifies something 
> higher.  The reason to do this is some devices can't wake the system 
> if they are in D3.  ACPI 3.0 has ways to indicate a desired power 
> state (not just maximum).  I don't have any evidence but fear some 
> devices won't work after resuming if set to D3 and they indicate this 
> with an _SxD so we always use the value in _SxD if present.
>
>> Is there any reason why adding something like
>>
>> if (state==3) {
>>     pci_set_power_state(dev,ACPI_STATE_D3COLD)
>> }
>>
>> to pci_device_suspend in the non-driver path and reenabling it in
>> pci_default_resume would result in things breaking?
>>
>> (Possibly with sanity checks as to whether it's a bridge or not)
>
>
> Not that I can think of.  You probably want state == S3 || S4 since 
> it's fine to power down devices for S4.  You'll probably find drivers 
> that don't properly resume their device.  You have to make sure you 
> power devices down after suspending them and power them up before 
> resuming them.
>


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