Re: [PATCH 4/4] USB: export autosuspend delay in sysfs

Am Freitag, 2. März 2007 17:27 schrieb Alan Stern:
> On Thu, 1 Mar 2007, Oliver Neukum wrote:
> 
> > Down an interface and it stays down. Suspend an interface and it ...
> 
> ... and it stays suspended until the kernel tries to send a packet out
> through that interface or until a packet is received (assuming proper
> hardware wakeup support is available and enabled).  That's pretty much
> exactly how I'd want my interface to behave if I was trying to save power.

That is how I expect autoconfig to work. If I suspend a device manually I
expect to to stay suspended until it say otherwise.

> > > Take a look at the definition of pm_message_t and tell me where you think
> > > the information could be stored.
> > 
> > How many in kernel data structures have been changed?
> 
> How many times have you succeeded in getting Pavel to change any of his 
> data structures?  :-)

I'll try voodoo. Or maybe I promise him a quadruped.

> > Though if we limit
> > pm to autosuspend the point is moot.
> 
> This boils down to one of our unanswered questions: How can we allow the
> user to suspend a device if the driver wants remote-wakeup capability but

Export the conditionality in sysfs? "NeedsRemoteWakeup" ?

> remote wakeup is disabled?  Autosuspend won't do it, for a simple reason:  
> Autosuspend is always supposed to be safe, and without remote wakeup
> it might not be safe.  We will need something stronger.
> 
> The other unanswered question is whether we need a separate attribute 
> (with separate permissions) for enabling/disabling autosuspend.  Note 
> that this attribute would be per-device and not per-interface, even if we 
> do have a per-interface delay attribute.

Yes, we need that.

> It would be nice if we could solve both questions together.  For example, 
> we might have a device attribute that would allow the superuser to:
> 
> 	Turn off autosuspend completely;
> 
> 	Allow autosuspend to operate normally, using the delay value
> 	specified in the other attribute file;
> 
> 	Force an immediate suspend, even if remote wakeup is disabled.

Have a delay attribute per interface and give each device an attribute
"SuspensionState" with the permissible values "on", "auto" & "suspend"
Handle RemoteWakeup as an orthogonal issue.

	Regards
		Oliver

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