Re: [RFC PATCH] PM / Runtime: Allow to inactivate devices during system suspend

[Kevin Hilman <khilman@linaro.org>]

Alan Stern <stern@rowland.harvard.edu> writes:

> On Tue, 19 Nov 2013, Ulf Hansson wrote:
>
>> At the moment, system PM is already affecting behaviour of runtime PM
>> since it is preventing runtime suspend during system suspend.
>
> Sure.  And that behavior is documented.  In any case, it's a bug for 
> drivers to depend on runtime suspend for carrying out a system suspend.

As Rafael mentioned, there is bus/pm_domain code that comes into play
here, so I'm not sure it's always a bug.

IMO, it's not a bug for the driver to depend on runtime PM if the
bus/pm_domain is handling the details.

On OMAP, we handle all the SoC on-chip devices with a pm_domain since
the low-level PM operations that need to happen are bus-level things not
device-level things.  Therefore, drivers for these devices can rely
entirely on runtime PM, even for system suspend.  The late/early
callbacks in the pm_domain can see if the device is runtime suspended
already or not and behave accordingly.

So, this all *can* work by handling it at the bus/pm_domain level, but
as Ulf has mentioned (and I agree) it seems like a clunky workaround
because the PM core is preventing it from happening as one might expect.

Kevin