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

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Date:   Mon, 6 Apr 2020 10:10:07 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Clément Péron <peron.clem@...il.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v2 0/7] Add support for Allwinner H6 DVFS

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.

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

> 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?

Maxime

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