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

Alan Cox
2010-05-27T17:49:18Z

> 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