Re: [RFC][PATCH 0/3] PCI PM: Rework pci_set_power_state

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On Friday, 20 of June 2008, Len Brown wrote:
> 
> > I've recently discovered that pci_set_power_state() calls the platform
> > callback intended for changing the state of the device after it has done
> > that using the native PCI mechanism.  In my opinion this is not correct,
> > because, for example, if the device is being put into D0 from a low power
> > state, it may require some platform-controlled power resources to be turned
> > on before that (in theory).
> > 
> > The following series of patches changes this function so that the platform
> > callback is performed first and then the native mechanism is used.
> > Additionally, however, it checks if the devices is power manageable by the
> > platform and only in that case the platform callback is invoked.  For this
> > purpose, I needed to add an ACPI function allowing PCI to check the power
> > manageability of given device.
> 
> We have 3 cases
> 1. device has PCI PM only
> 2. device has ACPI PM only
> 3. device has both PCI and ACPI PM
> 
> For #1 and #2, order is moot.
> For #3, how can we be sure that the new order is better than the old 
> order?  Is this a theoretical patch, or is there a failure case?

This was a theoretical patch, but please see the new series posted.

The difference is that in the new series the order is only changed for
transitions to D0.

Thanks,
Rafael
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