On Thursday, 21 June 2007 17:23, Alan Stern wrote:
> On Thu, 21 Jun 2007, Rafael J. Wysocki wrote:
>
> > > Just do 1). Global variables are ugly, and we already have space in
> > > pm_message_t.
> >
> > Well, this is what Len voted for, I think. David is against it.
> >
> > I also think that the cleanest way would be to pass that as an argument
> > to .suspend(), but currently pm_message_t. is passed by value and if we
> > made it a real struct (ie. with more than one field), that would also become
> > ugly, IMHO.
> >
> > So, can we make pm_message_t consist only of the target state?
>
> You're both repeating the mistakes from two years ago.
>
> You can't use a simple type to describe a target system state. While
> it might work for ACPI states, it won't work on general (i.e.,
> non-ACPI) systems.
I don't want to _describe_ system sleep states this way.
> It's probably a mistake even to use a data structure to describe a system
> state, since the requirements are so complex.
We already have defined two system sleep states that we think all of the
architectures may support: 'standby' and 'suspend'. Why don't we assign an
integer to each of them?
> The only reasonable approach is to describe it in code.
>
> What you can do is this: Pick a small enumerated set of labels for some
> selected system states. For example:
>
> enum pm_system_state {
> PM_STATE_RUNNING,
What for?
> PM_STATE_STANDBY,
> PM_STATE_SUSPEND,
> PM_STATE_HIBERNATE,
Different thing.
> };
>
> (It might be preferable to make the list more configurable, perhaps
> even allow changes at runtime. Never mind all that for now.)
Let me repeat: we _only_ need to tell drivers what the target system sleep
state will be. No less, no more.
We can do this using the existing pm_message_t, perhaps slightly modifying it,
or anything else, and in fact I don't care much what that will be. I'd only
prefer to use a .suspend() argument for this purpose, but if you think that
has to be a global variable for whatever practical reason, I'm fine with that
too.
> These are merely labels, they don't actually describe anything. To use
> them, you would have to pass them to a subsystem routine for
> interpretation. For example, pci_select_state() might pass one of
> these things to an ACPI routine, which would know what ACPI state
> corresponded to the given pm_system_state and would be able to say what
> D-state would be appropriate for a given PCI device. On a non-ACPI
> platform, pci_select_state() would have to call a different routine --
> something platform-dependent -- to do the same job.
>
>
> On the other hand, maybe you don't need anything like this at all.
> What would happen if a PCI driver put its device into a D-state which
> wasn't supported under the target ACPI state? Would it be so terrible?
> I can imagine that the requested wakeup functionality might not be
> available, but would it prevent the device from working properly when
> it was resumed?
Yes, I think so, in general.
Greetings,
Rafael
--
"Premature optimization is the root of all evil." - Donald Knuth
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