linux-kernel - Re: [PATCH v6 1/2] PM / Domains: Add support for 'required-opps' to set default perf state

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Date:   Wed, 11 Aug 2021 16:49:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>
Subject: Re: [PATCH v6 1/2] PM / Domains: Add support for 'required-opps' to
 set default perf state

On 11-08-21, 12:52, Ulf Hansson wrote:
> On Wed, 11 Aug 2021 at 12:07, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 11-08-21, 15:30, Rajendra Nayak wrote:
> > > In my case I don't want to error out if the property is missing, I want to error out
> > > only when the property exists but can't be translated into a performance state.
> > >
> > > So currently I check if the property exists and *only then* try to translate it, Ulf asked
> > > me to skip the check. If I do that and I call of_get_required_opp_performance_state()
> > > unconditionally, and if it errors out I will need to put in additional logic (check for
> > > return value of ENODEV) to distinguish between the property-does-not-exist vs
> > > property-exists-but-cannot-be-translated case.
> > > It just seems more straight-forward to call this only when the property exists, Ulf?
> >
> > The same check will be done by OPP core as well, so it is better to
> > optimize for the success case here. I will say, don't error out on
> > ENODEV, rest you know well.
> 
> This should work, while I generally favor not having to parse for
> specific return codes.
> 
> Another option is to add a new OPP OF helperfunction that just informs
> the caller whether the required-opps property exists (instead of
> open-coding that part), and if so, the caller can continue with
> of_get_required_opp_performance_state() and then expect it to succeed.
> 
> I have no strong opinion though! Whatever works for me.

I would like to work with the existing set of APIs, as the OPP core is
going to do that check anyways, again.

-- 
viresh