Re: [RFC v2 01/11] OPP: Don't overwrite rounded clk rate

[Rajendra Nayak]

On 6/17/2019 9:47 AM, Viresh Kumar wrote:
> On 17-06-19, 09:37, Rajendra Nayak wrote:
> > On 6/17/2019 9:20 AM, Viresh Kumar wrote:
> > > On 14-06-19, 10:57, Viresh Kumar wrote:
> > > > Hmm, so this patch won't break anything and I am inclined to apply it again :)
> > > >
> > > > Does anyone see any other issues with it, which I might be missing ?
> > >
> > > I have updated the commit log a bit more to clarify on things, please let me
> > > know if it looks okay.
> > >
> > >       opp: Don't overwrite rounded clk rate
> > >       The OPP table normally contains 'fmax' values corresponding to the
> > >       voltage or performance levels of each OPP, but we don't necessarily want
> > >       all the devices to run at fmax all the time. Running at fmax makes sense
> > >       for devices like CPU/GPU, which have a finite amount of work to do and
> > >       since a specific amount of energy is consumed at an OPP, its better to
> > >       run at the highest possible frequency for that voltage value.
> > >       On the other hand, we have IO devices which need to run at specific
> > >       frequencies only for their proper functioning, instead of maximum
> > >       possible frequency.
> > >       The OPP core currently roundup to the next possible OPP for a frequency
> > >       and select the fmax value. To support the IO devices by the OPP core,
> > >       lets do the roundup to fetch the voltage or performance state values,
> > >       but not use the OPP frequency value. Rather use the value returned by
> > >       clk_round_rate().
> > >       The current user, cpufreq, of dev_pm_opp_set_rate() already does the
> > >       rounding to the next OPP before calling this routine and it won't
> > >       have any side affects because of this change.
> >
> > Looks good to me. Should this also be documented someplace that dev_pm_opp_set_rate()
> > would not be able to distinguish between its users trying to scale CPU/GPU's vs IO
> > devices, so its the callers responsibility to round it accordingly before calling the
> > API?
>
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index 0fbc77f05048..bae94bfa1e96 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -751,8 +751,11 @@ static int _set_required_opps(struct device *dev,
>    * @dev:        device for which we do this operation
>    * @target_freq: frequency to achieve
>    *
> - * This configures the power-supplies and clock source to the levels specified
> - * by the OPP corresponding to the target_freq.
> + * This configures the power-supplies to the levels specified by the OPP
> + * corresponding to the target_freq, and programs the clock to a value <=
> + * target_freq, as rounded by clk_round_rate(). Device wanting to run at fmax
> + * provided by the opp, should have already rounded to the target OPP's
> + * frequency.
>    */

Perfect, thanks.

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