Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

[Alan Cox]

> What is a "Correctly implemented driver" in this case? One that receives 
> a wakeup event and then prevents suspend being entered until userspace 
> has acknowledged that event? Because that's what an in-kernel suspend 
> blocker is.

Kernel side maybe - but even then its a subset of expressing
latency/lowest level requirements. That bit isn't really too contentious.
You need a kernel object to hang a constraint off.

> ACPI provides no guarantees about what level of hardware functionality 
> remains during S3. You don't have any useful ability to determine which 
> events will generate wakeups. And from a purely practical point of view, 
> since the latency is in the range of seconds, you'll never have a low 
> enough wakeup rate to hit it.

So PCs with current ACPI don't get opportunistic suspend capability. It
probably won't be supported on the Commodore Amiga either - your point ?

> Suspend blockers are the mechanism for the 
> driver to indicate whether the wakeup event has been handled. That's 
> what they're there for. The in-kernel ones don't paper over anything.

Semantically the in kernel blockers and the in kernel expression of
device driven constraints are the same thing except that instead of 
yes/no you replace the boolean with information.


So we go from

	block_suspend() / unblock_suspend()

to
	add_pm_constraint(latency, level) 
	remove_pm_constraint(latency, level);


And if Android choses to interpret that in its policy code as

	if (latency > MAGIC)
		suspend_is_cool();
	else
		suspend_isnt_cool();

that's now isolated in droidspace policy

Alan


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/