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

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Date:   Tue, 30 Jul 2019 16:27:14 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>
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>,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        evgreen@...omium.org, 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 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.

> + * @avg_bw:    Average bandwidth in kilobytes per second
>   * @level:     Performance level
>   * @supplies:  Power supplies voltage/current values
>   * @clock_latency_ns: Latency (in nanoseconds) of switching to this OPP's
> @@ -81,6 +82,7 @@ struct dev_pm_opp {
>         bool suspend;
>         unsigned int pstate;
>         unsigned long rate;
> +       unsigned long avg_bw;
>         unsigned int level;
>
>         struct dev_pm_opp_supply *supplies;
> --
> 2.22.0.410.gd8fdbe21b5-goog
>