[PATCH 1/4] arm64: dts: imx8mm-venice-gw700x: override thermal cfg for industrial temp

[Jacky Bai]

> Subject: Re: [PATCH 1/4] arm64: dts: imx8mm-venice-gw700x: override
> thermal cfg for industrial temp
> 
> On 07.06.21 09:30, Jacky Bai wrote:
> >> Subject: Re: [PATCH 1/4] arm64: dts: imx8mm-venice-gw700x: override
> >> thermal cfg for industrial temp
> >>
> >> On 04.06.21 17:42, Tim Harvey wrote:
> >>> On Wed, Jun 2, 2021 at 12:11 AM Frieder Schrempf
> >>> <frieder.schrempf at kontron.de> wrote:
> >>>>
> >>>> On 01.06.21 19:49, Tim Harvey wrote:
> >>>>> Override the default temperature alert/crit for Industrial temp
> >>>>> IMX8M Mini.
> >>>>>
> >>>>> Signed-off-by: Tim Harvey <tharvey at gateworks.com>
> >>>>> ---
> >>>>>  .../boot/dts/freescale/imx8mm-venice-gw700x.dtsi     | 12
> >> ++++++++++++
> >>>>>  1 file changed, 12 insertions(+)
> >>>>>
> >>>>> diff --git
> >>>>> a/arch/arm64/boot/dts/freescale/imx8mm-venice-gw700x.dtsi
> >>>>> b/arch/arm64/boot/dts/freescale/imx8mm-venice-gw700x.dtsi
> >>>>> index c769fadbd008..512b76cd7c3b 100644
> >>>>> --- a/arch/arm64/boot/dts/freescale/imx8mm-venice-gw700x.dtsi
> >>>>> +++ b/arch/arm64/boot/dts/freescale/imx8mm-venice-gw700x.dtsi
> >>>>> @@ -493,3 +493,15 @@
> >>>>>               >;
> >>>>>       };
> >>>>>  };
> >>>>> +
> >>>>> +&cpu_alert0 {
> >>>>> +     temperature = <95000>;
> >>>>> +     hysteresis = <2000>;
> >>>>> +     type = "passive";
> >>>>> +};
> >>>>> +
> >>>>> +&cpu_crit0 {
> >>>>> +     temperature = <105000>;
> >>>>> +     hysteresis = <2000>;
> >>>>> +     type = "critical";
> >>>>> +};
> >>>>
> >>>> As this is not really board-specific, I think the proper way to
> >>>> handle this for
> >> all boards is to let the thermal driver read the temperature grading
> >> from the OTP fuses and set the trip-points accordingly, similar to
> >> what is done on i.MX6 [1].
> >>>>
> > ...
> >>>
> >>> Frieder,
> >>>
> >>> Yes, I thought about adding that kind of support to imx8mm_thermal.c
> >>> but the difference is that imx8mm has alerts defined by dt and imx6
> >>> does not so is it right to override dt alerts on imx8m? What if
> >>> someone designs a board that they specifically want a lower alert
> >>> than the cpu grade they are using based on something else on the board?
> >>>
> >>> My approach to this was to eventually actually adjust the imx8m dt
> >>> alerts in boot firmware based on some boot firmware setting or
> >>> specific board support and leave the kernel alone.
> >>
> >> Allowing board-specific trip points sounds like a valid request, but
> >> I still think we need a way to handle the temperature grading in the
> >> driver if no board-specific trip-points are given.
> >>
> >> What if we just set the temperature property in the trip nodes in
> >> imx8mm.dtsi to zero? The thermal driver would detect this and setup
> >> the correct values according to the grading. If the dt already
> >> provides non-zero temperature values (through the board dts) the
> >> driver will just leave the values and disregard the grading.
> >>
> >> I think this solution would be covering all needs.
> >
> > I thought to add the grading check in the imx8mm_thermal.c to
> > dynamically set the trip points temp, but it seems hard to do it due
> > to the fact of_thermal is used, as no helper API is exported by of_thermal,
> no better way to override the trip point temp.
> >
> > glad to see any good suggestions.
> 
> Right, the driver doesn't handle the trip-points directly. This is all hidden in the
> framework. So this might not be so easy to implement.
> 
> What about this other approach: Adding all the possible trip-points for the
> different gradings to the SoC-devicetree and then let the thermal driver
> remove the trip nodes from the dt that are not valid for the detected grading,
> just before the driver registers the sensor/zone.

It is more reasonable for the firmware/bootloader to handle this by checking the grading.

BR
Jacky Bai