Re: [PATCH v8 01/34] opp: Add dev_pm_opp_sync() helper

[Ulf Hansson <ulf.hansson@xxxxxxxxxx>]

On Wed, 18 Aug 2021 at 11:41, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Wed, 18 Aug 2021 at 11:14, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> >
> > On 18-08-21, 10:29, Ulf Hansson wrote:
> > > Me and Dmitry discussed adding a new genpd callback for this. I agreed
> > > that it seems like a reasonable thing to add, if he insists.
> > >
> > > The intent was to invoke the new callback from __genpd_dev_pm_attach()
> > > when the device has been attached to its genpd. This allows the
> > > callback, to invoke clk_get_rate() and then dev_pm_opp_set_rate(), to
> > > update the vote according to the current state of the HW.
> >
> > I wouldn't call dev_pm_opp_set_rate() from there, since it means
> > configure and enable (both) for different resources, clk, regulator,
> > genpd, etc..
>
> Right, good point!
>
> dev_pm_opp_set_rate() is best called from consumer drivers, as they
> need to be in control.
>
> >
> > What we need here is just configure. So something like this then:
> >
> > - genpd->get_performance_state()
> >   -> dev_pm_opp_get_current_opp() //New API
> >   -> dev_pm_genpd_set_performance_state(dev, current_opp->pstate);
> >
> > This can be done just once from probe() then.
>
> How would dev_pm_opp_get_current_opp() work? Do you have a suggestion?
>
> >
> > > I am not sure if/why that approach seemed insufficient?
> > >
> > > Another option to solve the problem, I think, is simply to patch
> > > drivers to let them call dev_pm_opp_set_rate() during ->probe(), this
> > > should synchronize the HW state too.
> >
> > Dmitry already mentioned that this will make the device start
> > consuming power, and he doesn't want that, else we need an explicit
> > disble call as well.
>
> I am sure I understand the problem. When a device is getting probed,

/s/I am sure/I am not sure

> it needs to consume power, how else can the corresponding driver
> successfully probe it?
>
> >
> > --
> > viresh
>
> Kind regards
> Uffe