Re: #thermal-sensor-cells under protocol@15

(Ignoring disclaimer assuming it was a mistake, get it fixed for the next time)

On Tue, Jul 28, 2026 at 11:53:41AM +0200, Laszlo Ersek wrote:
> Hello,
> 
> as of commit 62cc90241548 («Merge tag
> 'mm-hotfixes-stable-2026-07-27-14-18' of
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm», 2026-07-27):
> 
> "Documentation/devicetree/bindings/firmware/arm,scmi.yaml" specifies
> that for protocol@15 -- the SCMI Sensor management protocol --, property
> #thermal-sensor-cells is required (with value 1).
> 

Correct.

> I don't understand this requirement. According to now-historical commit
> fe7be8b297b2 («dt-bindings: arm: add support for ARM System Control and
> Management Interface(SCMI) protocol», 2018-02-28), #thermal-sensor-cells
> specifies the width of SCMI "Sensor ID"s used in sensor references made
> by "thermal-sensors".
> 

Indeed.

> But a platform's complete set of sensors may not contain a single
> thermal sensor (only other sensor types). In that case, the driver file
> 
>   drivers/thermal/thermal_of.c
> 
> has no business connecting to SCMI (= no business referring to Sensor
> IDs; consequently, the width of a Sensor ID is irrelevant), while the
> driver file
> 

Sure. I assume you don't have any "thermal-sensors" defined in the platform
device tree.

>   drivers/hwmon/scmi-hwmon.c
> 
> may still justifiedly want to consume protocol@15 (SCMI_PROTOCOL_SENSOR)
> from the device tree (i.e., to expose SCMI-provided sensors -- *not*
> thermal sensors -- via the hwmon interface, to usespace).
> 

OK, but I don't understand the exact problem you are facing.

> And so describing protocol@15 in the Device Tree, without a
> #thermal-sensor-cells property, looks like a valid use case.
> 

No, unless you go back in time and find a replacement for #thermal-sensor-cells
and replace it w/o breaking any compatibility.

> Am I wrong?
> 

We need some property cell to be set to 1 to read the SCMI IDs. For backward
compatibility reasons, it will remain #thermal-sensor-cells.

> Thanks!
> Laszlo
> IMPORTANT NOTICE: The contents of this email and any attachments are
> confidential and may also be privileged. If you are not the intended
> recipient, please notify the sender immediately and do not disclose the
> contents to any other person, use it for any purpose, or store or copy the
> information in any medium. Thank you.


Deleted now, please fix it for next time.

-- 
Regards,
Sudeep