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Date:   Mon, 21 Feb 2022 10:38:38 -0800
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To:     Jon Hunter <jonathanh@nvidia.com>,
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From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v3 2/4] hwmon: (lm90) Use hwmon_notify_event()
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On 2/21/22 08:22, Jon Hunter wrote:
> 
> On 21/02/2022 16:16, Jon Hunter wrote:
>>
>> On 21/02/2022 16:02, Guenter Roeck wrote:
>>
>> ...
>>
>>>> The platform I see this on does use device-tree and it does have a node for the ti,tmp451 device which uses the lm90 device. This platform uses the device-tree source arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts and the tmp451 node is in arch/arm64/boot/dts/nvidia/tegra194-p2888.dtsi.
>>>>
>>>
>>> Interesting. It appears that the call to devm_thermal_zone_of_sensor_register()
>>> in the hwmon core nevertheless returns -ENODEV which is not handled properly
>>> in the hwmon core. I can see a number of reasons for this to happen:
>>> - there is no devicetree node for the lm90 device
>>> - there is no thermal-zones devicetree node
>>> - there is no thermal zone entry in the thermal-zones node which matches
>>>    the sensor
>>
>>
>> So we definitely have the node for the lm90 device and a thermal-zones node, but I do not see a thermal-sensor node. Maybe this is what we are missing?
> 
> Actually, that is not true. We do have thermal-sensor nodes in arch/arm64/boot/dts/nvidia/tegra194.dtsi.
> 

There is probably a zone to sensor id mismatch. hwmon sends the sensor index
as sensor_id to the thermal subsystem. Those sensor IDs would be 0, 1, and
possibly 2 for the lm90 driver. Assuming this should match the thermal-sensors
values in arch/arm64/boot/dts/nvidia/tegra194.dtsi, those start with 2,
so there would be a likely mismatch. Also, all those dtsi entries match
against pbmp/thermal, not against the lm90 sensor(s).

Thanks,
Guenter