Re: PCI power state mapping

[Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>]

Hi!

> As far as I know the kernel has three different power modes. The ACPI 
> ones (S0-S5), the linux ones (PM_SUSPEND_*) and the PCI ones (D0-D3). 
> Mapping between the first two is done by the ACPI routines. But 
> mapping between kernel power states and PCI is not done at all. The 
> PM-enumerations are propagated all the way down to 
> pci_set_power_state(). I.e. the function expects PCI states but gets 

I have patch that converts all this to enums, and introduces
to_pci_state() function. That should solve part of confusion.


> Now for the problem. Most PCI devices do not support state D1 and D2 
> (which would be called when entering PM_SUSPEND_STANDBY or 
> PM_SUSPEND_MEM). This causes the pci_set_power_state() to fail and 
> the suspend to be aborted. I haven't found any good documentation 
> about the PCI power states but from what I can gather D0 is full 
> power, D1-D2 are used during normal operation to conserve some power 
> (when the device is idle I guess) and D3 when it enters some form of 
> suspend. So PM_SUSPEND_MEM should probably put the devices in D3, not 
> D2. Microsoft seem to increase the state until it finds on the device 
> supports:

Okay, to_pci_state will have to be fixed.

> Windows has something called system-to-device (SxD) mapping which 
> seems to handle most of this. I can't find the equivalent in linux 
> ACPI implementation. To me, this looks like a rather crucial part of 
> the system.

Someone will need to write that one...
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