On Thu, 30 Mar 2023 at 11:34, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
>
> On Thu, Mar 30, 2023 at 02:12:49PM +0530, Maulik Shah wrote:
> > A switch from OSI to PC mode is only possible if all CPUs other than the
> > calling one are OFF, either through a call to CPU_OFF or not yet booted.
> >
>
> As per the spec, all cores are in one of the following states:
> - Running
> - OFF, either through a call to CPU_OFF or not yet booted
> - Suspended, through a call to CPU_DEFAULT_SUSPEND
>
> Better to provide full information.
>
> > Currently OSI mode is enabled before power domains are created. In cases
> > where CPUidle states are not using hierarchical CPU topology the bail out
> > path tries to switch back to PC mode which gets denied by firmware since
> > other CPUs are online at this point and creates inconsistent state as
> > firmware is in OSI mode and Linux in PC mode.
> >
>
> OK what is the issue if the other cores are online ? As long as they are
> running, it is allowed in the spec, so your statement is incorrect.
>
> Is CPUidle enabled before setting the OSI mode. I see only that can cause
> issue as we don't use CPU_DEFAULT_SUSPEND. If idle is not yet enabled, it
> shouldn't be a problem.
Sudeep, you may very well be correct here. Nevertheless, it looks like
the current public TF-A implementation doesn't work exactly like this,
as it reports an error in Maulik's case. We should fix it too, I
think.
Although, to me it doesn't really matter as I think $subject patch
makes sense anyway. It's always nice to simplify code when it's
possible.
Note also that, before commit 70c179b49870 ("cpuidle: psci: Allow PM
domain to be initialized even if no OSI mode"), it made sense to call
psci_pd_try_set_osi_mode() before creating the genpds, but beyond that
it doesn't really matter anymore.
Kind regards
Uffe
