linux-kernel - Re: [PATCH v3 2/6] OPP: Add support for bandwidth OPP tables

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Date:   Tue, 30 Jul 2019 16:20:59 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Sweeney, Sean" <seansw@....qualcomm.com>,
        David Dai <daidavid1@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] OPP: Add support for bandwidth OPP tables

On Tue, Jul 30, 2019 at 3:57 AM Amit Kucheria <amit.kucheria@...aro.org> wrote:
>
> On Wed, Jul 3, 2019 at 6:40 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > Not all devices quantify their performance points in terms of frequency.
> > Devices like interconnects quantify their performance points in terms of
> > bandwidth. We need a way to represent these bandwidth levels in OPP. So,
> > add support for parsing bandwidth OPPs from DT.
> >
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >  drivers/opp/of.c  | 34 ++++++++++++++++++++++++++++++++--
> >  drivers/opp/opp.h |  4 +++-
> >  2 files changed, 35 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> > index c10c782d15aa..54fa70ed2adc 100644
> > --- a/drivers/opp/of.c
> > +++ b/drivers/opp/of.c
> > @@ -552,6 +552,35 @@ void dev_pm_opp_of_remove_table(struct device *dev)
> >  }
> >  EXPORT_SYMBOL_GPL(dev_pm_opp_of_remove_table);
> >
> > +static int _read_opp_key(struct dev_pm_opp *new_opp, struct device_node *np)
> > +{
> > +       int ret;
> > +       u64 rate;
> > +       u32 bw;
> > +
> > +       ret = of_property_read_u64(np, "opp-hz", &rate);
> > +       if (!ret) {
> > +               /*
> > +                * Rate is defined as an unsigned long in clk API, and so
> > +                * casting explicitly to its type. Must be fixed once rate is 64
> > +                * bit guaranteed in clk API.
> > +                */
> > +               new_opp->rate = (unsigned long)rate;
> > +               return 0;
> > +       }
> > +
> > +       ret = of_property_read_u32(np, "opp-peak-KBps", &bw);
> > +       if (ret)
> > +               return ret;
> > +       new_opp->rate = (unsigned long) &bw;
> > +
> > +       ret = of_property_read_u32(np, "opp-avg-KBps", &bw);
> > +       if (!ret)
> > +               new_opp->avg_bw = (unsigned long) &bw;
> > +
> > +       return 0;
> > +}
> > +
> >  /**
> >   * _opp_add_static_v2() - Allocate static OPPs (As per 'v2' DT bindings)
> >   * @opp_table: OPP table
> > @@ -589,11 +618,12 @@ static struct dev_pm_opp *_opp_add_static_v2(struct opp_table *opp_table,
> >         if (!new_opp)
> >                 return ERR_PTR(-ENOMEM);
> >
> > -       ret = of_property_read_u64(np, "opp-hz", &rate);
> > +       ret = _read_opp_key(new_opp, np);
> >         if (ret < 0) {
> >                 /* "opp-hz" is optional for devices like power domains. */
> >                 if (!opp_table->is_genpd) {
> > -                       dev_err(dev, "%s: opp-hz not found\n", __func__);
> > +                       dev_err(dev, "%s: opp-hz or opp-peak-bw not found\n",
> > +                               __func__);
> >                         goto free_opp;
> >                 }
> >
> > diff --git a/drivers/opp/opp.h b/drivers/opp/opp.h
> > index 569b3525aa67..ead2cdafe957 100644
> > --- a/drivers/opp/opp.h
> > +++ b/drivers/opp/opp.h
> > @@ -59,7 +59,8 @@ extern struct list_head opp_tables;
> >   * @turbo:     true if turbo (boost) OPP
> >   * @suspend:   true if suspend OPP
> >   * @pstate: Device's power domain's performance state.
> > - * @rate:      Frequency in hertz
> > + * @rate:      Frequency in hertz OR Peak bandwidth in kilobytes per second
>
> rate is most often used for clk rates. Let us not overload this just
> to save one struct member. IMO, you should introduce a peak_bw member
> and then have an error check if the DT provides both rate and peak_bw
> during parsing.

This is not about saving space. It avoids having to rewrite a lot of
helper functions. If you want, I can rename this to "key" but I'm not
going to create a different field.

-Saravana