Re: [linux-pm] [PATCH 00/04][RFC] PM: Runtime platform device PM

[Magnus Damm <magnus.damm@gmail.com>]

Hi Pavel!

On Wed, Jun 3, 2009 at 6:37 AM, Pavel Machek <pavel@ucw.cz> wrote:
>> > In the process of discussing a similar interface for OMAP, we dicussed
>> > that having 3 states would be more useful.  Specifically, and
>> > _enable(), _idle() and _disable() hook.  The _enable() and _idle()
>> > hooks being exactly what you proposed above, but with the addition of
>> > a _disable() hook which says not only can the device go idle, but that
>> > the driver is really finished with the device.  In this case, more
>> > aggresive PM measures could be taken, such as turning of regulators
>> > that may have long latencies that may not be appropriate to turn off
>> > in idle.
>>
>> Hm.. I wonder when the driver is really finished with the device
>> though. Only when the module is unloaded? If so then we could deal
>> with the hard disable using platform bus notifiers (like in [04/04]).
>
> I'd guess that they call disable() when /dev node is closed... and
> idle() when device is opened but inactive.

But the time from close() to next open() is work load dependent. So
the difference between _disable() and _idle() is pretty fuzzy in my
opinion. I'm trying to think of a case where hard _disable() is
needed, but nothing comes to mind.

In my mind a single disable()/idle() function together with latency
information is enough. It covers the entire range from _idle() to hard
_disable().

/ magnus