Re: [PATCH 1/2] ARM: dts: rockchip: Limit GPU frequency on veyron mickey to 300 MHz when the CPU gets very hot

[Doug Anderson]

Hi,

On Mon, May 20, 2019 at 10:01 AM Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote:
>
> On rk3288 the CPU and GPU temperatures are correlated. Limit the GPU
> frequency on veyron mickey to 300 MHz for CPU temperatures >= 85ÂC.
>
> This matches the configuration of the downstream Chrome OS 3.14 kernel,
> the 'official' kernel for mickey.
>
> Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> ---
> Note: this patch depends on "ARM: dts: rockchip: Add #cooling-cells
> entry for rk3288 GPU" (https://lore.kernel.org/patchwork/patch/1075005/)
> ---
>  arch/arm/boot/dts/rk3288-veyron-mickey.dts | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/rk3288-veyron-mickey.dts b/arch/arm/boot/dts/rk3288-veyron-mickey.dts
> index d889ab3c8235..f118d92a49d0 100644
> --- a/arch/arm/boot/dts/rk3288-veyron-mickey.dts
> +++ b/arch/arm/boot/dts/rk3288-veyron-mickey.dts
> @@ -125,6 +125,12 @@
>                                          <&cpu2 8 THERMAL_NO_LIMIT>,
>                                          <&cpu3 8 THERMAL_NO_LIMIT>;
>                 };
> +
> +               /* At very hot, don't let GPU go over 300 MHz */
> +               cpu_very_hot_limit_gpu {
> +                       trip = <&cpu_alert_very_hot>;
> +                       cooling-device = <&gpu 2 2>;
> +               };

Two things:

A) If I'm reading things properly, you're actually limiting things to
400 MHz.  This is because you don't have <https://crrev.com/c/1574579>
which deletes the 500 MHz GPU operating point.  So on upstream the
available points are:

0: 600 MHz
1: 500 MHz
2: 400 MHz
3: 300 MHz
4: 200 MHz
5: 100 MHz

...and downstream:

0: 600 MHz
1: 400 MHz
2: 300 MHz
3: 200 MHz
4: 100 MHz

Thinking about it more, I bet Heiko would actually be OK deleting the
500 MHz GPU operating point for veyron.  Technically it's not needed
upstream because upstream doesn't have our hacks to allow re-purposing
NPLL for HDMI (so they _can_ make 500 MHz) but maybe we can make the
argument that these laptops have only ever been tested with the 500
MHz operating point removed and also that eventually someonje will
probably figure out a way to re-purpose NPLL for HDMI even upstream...


B) It seems like in the same patch you'd want to introduce
"cpu_warm_limit_gpu", AKA:

cpu_warm_limit_gpu {
  trip = <&cpu_alert_warm>;
  cooling-device =
  <&gpu 1 1>;
};


-Doug