linux-kernel - Re: [PATCH v7 6/7] OPP: Update the bandwidth on OPP frequency changes

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Date:   Thu, 30 Apr 2020 13:23:56 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Sibi Sankar <sibis@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Evan Green <evgreen@...omium.org>,
        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 v7 6/7] OPP: Update the bandwidth on OPP frequency changes

On 30-04-20, 00:35, Saravana Kannan wrote:
> On Wed, Apr 29, 2020 at 11:09 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > On 24-04-20, 14:18, Saravana Kannan wrote:
> > > My only comment is -- can we drop this patch please? I'd like to use
> > > devfreq governors for voting on bandwidth and this will effectively
> > > override whatever bandwidth decisions are made by the devfreq
> > > governor.
> >
> > And why would that be better ? FWIW, that will have the same problem
> > which cpufreq governors had since ages, i.e. they were not proactive
> > and were always too late.
> >
> > The bw should get updated right with frequency, why shouldn't it ?
> 
> I didn't say the bw would be voted based on just CPUfreq. It can also
> be based on CPU busy time and other stats. Having said that, this is
> not just about CPUfreq. Having the bw be force changed every time a
> device has it's OPP is changed is very inflexible. Please don't do it.

So, the vote based on the requirements of cpufreq driver should come
directly from the cpufreq side itself, but no one stops the others
layers to aggregate the requests and then act on them. This is how it
is done for other frameworks like clk, regulator, genpd, etc.

You guys need to figure out who aggregates the requests from all users
or input providers for a certain path. This was pushed into the genpd
core in case of performance state for example.

-- 
viresh