linux-kernel - Re: [PATCH v2 0/7] Add support for Allwinner H6 DVFS

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Date:   Mon, 6 Apr 2020 11:07:44 +0200
From:   Clément Péron <peron.clem@...il.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v2 0/7] Add support for Allwinner H6 DVFS

Hi Maxime,

On Mon, 6 Apr 2020 at 10:10, Maxime Ripard <maxime@...no.tech> wrote:
>
> Hi,
>
> On Sun, Apr 05, 2020 at 07:35:54PM +0200, Clément Péron wrote:
> > Now that required drivers are merged we can contibute on DVFS
> > support for Allwinner H6.
> >
> > This serie is based on Yangtao Li serie[0] and Ondřej Jirman work[1].
> >
> > Most of the OPP tables are taken from original vendor kernel[2].
> > Plus there is a new CPU frequencies at 1.6GHz, 1.7GHz and 1.8GHz.
> >
> > I wrote a simple script to randomly set a frequency during
> > a random time[3].
>
> If you ever need to do that ever again, cpufreq-ljt-stress-test (found
> here https://github.com/ssvb/cpuburn-arm) has proven to be very
> reliable to detect cpufreq related issues. stress-ng might not be
> enough since the (at least older) Allwinner SoCs tend to create cache
> corruption when undervolted, and that might not be unnoticed by
> stress-ng but will be catched by cpufreq-ljt-stress-test.

Thanks for the tool and explanation. I will test the v3 with this one.

>
> Also, it will test each frequency, while random frequencies might skip
> a few.

I didn't count them but there was more than 2000lines, probability to miss
a frequency is really low. Also changing from 500MHz to 1.8GHz could have
trigger some out-of-spec issue.

But just to be sure I will add an init phase before doing random stuff.

>
> > With this script and using stress-ng during several hours, I didn't
> > see any issue. Moreover I have tested specifically the 1.8GHz on my
> > Beelink GS1, max thermal 85°C is reached very quickly and then the
> > SoC oscillates quickly between 1.5 and 1.8GHz. So i have added
> > 1.6GHz and 1.7GHz my board now oscillate slower between 1.5GHz and
> > 1.6GHz swapping every second and temperature is also morestable.
> >
> > I also test that that offlining CPU0 and doing DVFS on other CPUs
> > works. As CPU regulator is only set for CPU0.
> >
> > But maybe it doesn't cost much to set the regulator for all the CPUs?
> >
> > Jernej test the GPU devfreq on several H6 board particulary the
> > Tanix TX6 which doesn't have a proper dedicated PMIC and doesn't
> > had any trouble with it.
> >
> > Do you think I can enable GPU OPP for all H6 Boards?
>
> It seems you're doing it?
No I don't, see my answer on patch 4/7.

Thanks for your review,
Clément

>
> Maxime