linux-kernel - Re: [PATCH v3 1/6] dt-bindings: opp: Introduce opp-peak-KBps and opp-avg-KBps bindings

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Date:   Tue, 23 Jul 2019 17:18:31 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Sibi Sankar <sibis@...eaurora.org>,
        Georgi Djakov <georgi.djakov@...aro.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>,
        daidavid1@...eaurora.org, Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux PM <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 1/6] dt-bindings: opp: Introduce opp-peak-KBps and
 opp-avg-KBps bindings

On Tue, Jul 23, 2019 at 7:27 AM Rob Herring <robh@...nel.org> wrote:
>
> On Mon, Jul 22, 2019 at 5:41 PM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Mon, Jul 22, 2019 at 4:35 PM Rob Herring <robh@...nel.org> wrote:
> > >
> > > On Tue, Jul 16, 2019 at 11:58:08AM -0700, Saravana Kannan wrote:
> > > > On Tue, Jul 16, 2019 at 10:25 AM Sibi Sankar <sibis@...eaurora.org> wrote:
> > > > >
> > > > > Hey Saravana,
> > > > >
> > > > > https://patchwork.kernel.org/patch/10850815/
> > > > > There was already a discussion ^^ on how bandwidth bindings were to be
> > > > > named.
> > > >
> > > > Yes, I'm aware of that series. That series is trying to define a BW
> > > > mapping for an existing frequency OPP table. This patch is NOT about
> > > > adding a mapping to an existing table. This patch is about adding the
> > > > notion of BW OPP tables where BW is the "key" instead of "frequency".
> > > >
> > > > So let's not mixed up these two series.
> > >
> > > Maybe different reasons, but in the end we'd end up with 2 bandwidth
> > > properties. We need to sort out how they'd overlap/coexist.
> >
> > Oh, I totally agree! My point is that the other mapping isn't the
> > right approach because it doesn't handle a whole swath of use cases.
> > The one I'm proposing can act as a super set of the other (as in, can
> > handle that use case too).
> >
> > > The same comment in that series about defining a standard unit suffix
> > > also applies to this one.
> >
> > I thought I read that whole series and I don't remember reading about
> > the unit suffix. But I'll take a closer look. I've chosen to keep the
> > DT units at least as "high of a resolution" as what the APIs accept
> > today. The APIs take KB/s. So I make sure DT can capture KB/s
> > differences. If we all agree that KB/s is "too accurate" then I think
> > we should change everything to MB/s.
>
> Either one is fine with me, but trying to align to what the OS picked
> doesn't work. What does BSD use for example? More important is
> aligning across DT properties so we don't have folks picking whatever
> random unit they like. We generally try to go with the smallest units
> that will have enough (32-bit) range for everyone, so that's probably
> KB/s here.

Yeah, that makes sense.

-Saravana