[PATCH V4 1/2] dt-bindings: thermal: add support for Broadcom's Northstar thermal

[Jon Mason]

On Sun, Apr 2, 2017 at 11:07 PM, Jon Mason <jon.mason at broadcom.com> wrote:
> On Sat, Apr 1, 2017 at 5:50 PM, Rafał Miłecki <zajec5 at gmail.com> wrote:
>> On 04/01/2017 09:51 PM, Eduardo Valentin wrote:
>>>
>>> On Fri, Mar 31, 2017 at 10:11:23PM +0200, Rafał Miłecki wrote:
>>>>
>>>> From: Rafał Miłecki <rafal at milecki.pl>
>>>>
>>>> This commit documents binding for thermal used in Northstar family SoCs.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
>>>> ---
>>>> V3: Add thermal-zones to the example
>>>>     Rob: Because of this update, I didn't include Acked-by I got for V2
>>>> ---
>>>>  .../devicetree/bindings/thermal/brcm,ns-thermal    | 26
>>>> ++++++++++++++++++++++
>>>>  1 file changed, 26 insertions(+)
>>>>  create mode 100644
>>>> Documentation/devicetree/bindings/thermal/brcm,ns-thermal
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/thermal/brcm,ns-thermal
>>>> b/Documentation/devicetree/bindings/thermal/brcm,ns-thermal
>>>> new file mode 100644
>>>> index 000000000000..c561c7349f17
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/thermal/brcm,ns-thermal
>>>> @@ -0,0 +1,26 @@
>>>> +* Broadcom Northstar Thermal
>>>> +
>>>> +This binding describes thermal sensor that is part of Northstar's DMU
>>>> (Device
>>>> +Management Unit).
>>>> +
>>>> +Required properties:
>>>> +- compatible : Must be "brcm,ns-thermal"
>>>> +- reg : iomem address range of PVTMON registers
>>>> +- #thermal-sensor-cells : Should be <0>
>>>> +
>>>> +Example:
>>>> +
>>>> +thermal: thermal at 1800c2c0 {
>>>> +       compatible = "brcm,ns-thermal";
>>>> +       reg = <0x1800c2c0 0x10>;
>>>> +       #thermal-sensor-cells = <0>;
>>>> +};
>>>> +
>>>> +thermal-zones {
>>>> +       cpu_thermal: cpu-thermal {
>>>> +               polling-delay-passive = <0>;
>>>> +               polling-delay = <1000>;
>>>> +               coefficients = <(-556) 418000>;
>>>> +               thermal-sensors = <&thermal>;
>>>
>>>
>>> You need to define trips and cooling devices here. Otherwise, makes
>>> little sense to have this device in thermal subsystem. Here is an
>>> example of minimal set:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal.git/commit/?h=linus&id=1e2ac9821de6a85d3e8358f238436708d1d46869
>>>
>>> The above has no passive action. It is just gonna shutdown the system if
>>> temperature crosses a threshold.
>>>
>>> But, a typical cooling device would be CPU frequency throttling. Do you
>>> have
>>> that up and running in your routers?
>>
>>
>> I don't have CPU freq throttling, so shutdown will be the only solution for
>> critical temp right now.
>>
>> I know I should have at least a trip for critical temperature, but the
>> problem
>> is I don't know what value to use. There isn't any info about this in public
>> datasheets. Broadcom's SDK doesn't mention it. Vendors share only the max
>> environment temp, not the max CPU temp.
>>
>> So for now I only meant to provide user space access to reading current CPU
>> temperature. I could do some stress tests and ask other users to do it as
>> well.
>>
>> Or maybe I could just put in Documentation some round value that makes more
>> or
>> less sense and then work on a proper content of real DTS files?
>>
>> Unless we can get some hint from Broadcom people. Jon? Florian? Anyone?
>
> I'll poke around and see if I can find a datasheet for NS/NSP.  Worst
> case, I can ask one of the HW engineers for NSP, and we can use the
> same value for NS.

In the NS documentation, under "Absolute Maximum Ratings":

The "Maximum Junction Temperature" is 125 C
The "Commercial Ambient Temperature (Operating)" range is 0 to 75 C
The "Industrial  Ambient Temperature (Operating)" range is -40 to 85 C
The "Storage Temperature" range is -40 to 125 C

In the NSP documentation, under "Absolute Maximum Ratings":

The "Maximum Junction Temperature" is 110 C
The "Commercial Ambient Temperature (Operating)" range is 0 to 75 C
The "Industrial  Ambient Temperature (Operating)" range is -40 to 85 C
The "Storage Temperature" range is -40 to 125 C

I believe the first one is the number you are looking for.

Thanks,
Jon