Re: [RFC PATCH 3/3] cpuidle: psci: Initialize the PM domains in powered off state for OSI

On 26-08-19 17:14:53, Ulf Hansson wrote:
> From: Ulf Hansson <[email protected]>
> 
> At the point when the PM domain and the topology are registered through the
> genpd subsystem, it's not really known whether corresponding CPUs are
> online and thus if the PM domain should be initialized as powered on or
> not. Instead this information becomes available when the CPU devices gets
> attached to their respective PM domain through dt_idle_attach_cpu().
> 
> This is a problem when using PSCI OS-initiated mode, as we may end up with
> a PM domain that has the genpd's status indicating it to be powered on,
> while it in fact may not be the case. In the less severe scenario, this
> leads to selecting a shallower domain idle state for the PM domain than
> necessary. A more critical problem is when a non-CPU device shares the PM
> domain, leading to their corresponding drivers not being able to trust the
> status of it.

Exactly why a third state like GENPD_STATE_UNKNOWN would be more
fitting, IMO. Maybe something we can do at some point.

This solution works for now as well.

> 
> Let's fix these problems by initializing the state for the genpd's to be
> powered off and in the deepest possible domain idle state, when using
> OS-initiated mode. The support for ->sync_state() is maintained by setting
> the GENPD_FLAG_OFF_STAY_ON for the genpds in question.
> 
> Reported-by: Maulik Shah <[email protected]>
> Link: https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Ulf Hansson <[email protected]>

Reviewed-by: Abel Vesa <[email protected]>