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

From: Adam Ford <aford173@gmail.com>
To: "H. Nikolaus Schaller" <hns@goldelico.com>
Cc: "Nishanth Menon" <nm@ti.com>,
	Linux-OMAP <linux-omap@vger.kernel.org>,
	"Tony Lindgren" <tony@atomide.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"André Roth" <neolynx@gmail.com>,
	"Discussions about the Letux Kernel"
	<letux-kernel@openphoenux.org>
Subject: Re: [Letux-kernel] [RFC PATCH 0/3] Enable 1GHz support on omap36xx
Date: Thu, 12 Sep 2019 13:52:06 -0500	[thread overview]
Message-ID: <CAHCN7xK=4JusZ-6r0qe0SBBb0KzVBguXWtw236kO5UQ4F=Jsig@mail.gmail.com> (raw)
In-Reply-To: <CAHCN7xJgOhCpsiSvxOHeRz+621+t53pyt4_iE1PNCigznb1GLw@mail.gmail.com>

On Thu, Sep 12, 2019 at 8:58 AM Adam Ford <aford173@gmail.com> wrote:
>
> On Wed, Sep 11, 2019 at 12:49 PM Adam Ford <aford173@gmail.com> wrote:
> >
> > On Wed, Sep 11, 2019 at 12:43 PM H. Nikolaus Schaller <hns@goldelico.com> wrote:
> > >
> > > Hi Adam,
> > >
> > > > Am 11.09.2019 um 18:01 schrieb H. Nikolaus Schaller <hns@goldelico.com>:
> > > >
> > > >>
> > > >> Am 11.09.2019 um 17:56 schrieb Adam Ford <aford173@gmail.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.

I submitted an RFC for thermal throttling.  I am not sure if I did it
right, and I don't have a good way to test it.

adam

> >
> > We're almost there!
> >
> > adam
> > >
> > > BR,
> > > Nikolaus
> > >