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

Ulf Hansson
2021-08-18T09:42:10Z

On Wed, 18 Aug 2021 at 11:14, Viresh Kumar <viresh.kumar@linaro.org> 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,
it needs to consume power, how else can the corresponding driver
successfully probe it?

>
> --
> viresh

Kind regards
Uffe