linux-kernel - Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx

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Message-ID: <CAHCN7xJgOhCpsiSvxOHeRz+621+t53pyt4_iE1PNCigznb1GLw@mail.gmail.com>
Date:   Thu, 12 Sep 2019 08:58:20 -0500
From:   Adam Ford <aford173@...il.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Nishanth Menon <nm@...com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        André Roth <neolynx@...il.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx

On Wed, Sep 11, 2019 at 12:49 PM Adam Ford <aford173@...il.com> wrote:
>
> On Wed, Sep 11, 2019 at 12:43 PM H. Nikolaus Schaller <hns@...delico.com> wrote:
> >
> > Hi Adam,
> >
> > > Am 11.09.2019 um 18:01 schrieb H. Nikolaus Schaller <hns@...delico.com>:
> > >
> > >>
> > >> Am 11.09.2019 um 17:56 schrieb Adam Ford <aford173@...il.com>:
> > >>
> > >>> There are some subtleties for testing.
> > >>>
> > >>> * I have added turbo-mode; to OPP6 / OPP1G
> > >>> * which means they are available but not used by the ondemand govenor
> > >>> * to enable them one has to echo 1 >/sys/devices/system/cpu/cpufreq/boost
> > >>
> > >> Will that be documented somewhere? If not, can we put a comment in the
> > >> device tree so people know how to enable it?
> > >
> > > It seems to be pretty standard on i86 systems if you google for "turbo mode".
> > > I have added it to the commit message which adds the vbb regulator.
> >
> > And, I am not sure if DT maintainers will accept comments about the
> > Linux /sys implementation in device tree files or bindings. Those
> > should be independent of Linux.
>
> OK.
> >
> > Basically the turbo-mode property is a hint to the OPP system (which
> > may or may not use of it).
> >
> > So I think it is indeed better to have it in the commit message and
> > not the code.
>
> That makes sense.
>
> >
> > One more thought: as long as we do not have junction temperature monitoring
> > we should keep it off by default... We may even remove the turbo-mode
> > designator if we have the 90°C limit and smart reflex working.

I found some info on the thermal framework [1].  It seems to show that
we can put placeholders in the device tree to help facilitate this.

An excerpt from [1]  shows:
     Cooling devices provide control on power dissipation.
     There are essentially two ways to provide control on power dissipation.
     First is by means of regulating device performance, which is
known as passive cooling (DVFS).
     ... [snip stuff about cooling fans]

It also shows there are ways to link the cpu node to the cooling info.
Since it shows DVFS can be used to regulate temperature, it seems like
the hooks might already be in place

[1] - https://blog.linuxplumbersconf.org/2015/ocw//system/presentations/2613/original/thermal-framework-status-no-transitioning.pdf

The downside is that the OMAP thermal sensor is unreliable.
>
> We're almost there!
>
> adam
> >
> > BR,
> > Nikolaus
> >