linux-kernel - Re: [PATCH v3 1/5] Documentation: add DT bindings for ARM SCPI sensors

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Message-ID: <9hhk2rtdq1f.fsf@e105922-lin.cambridge.arm.com>
Date:	Mon, 14 Sep 2015 15:38:36 +0100
From:	Punit Agrawal <punit.agrawal@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"linux-pm\@vger.kernel.org" <linux-pm@...r.kernel.org>,
	"lm-sensors\@lm-sensors.org" <lm-sensors@...sensors.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	"edubezval\@gmail.com" <edubezval@...il.com>,
	"linux\@roeck-us.net" <linux@...ck-us.net>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"robh+dt\@kernel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH v3 1/5] Documentation: add DT bindings for ARM SCPI sensors

Mark Rutland <mark.rutland@....com> writes:

>> >> +Sensor bindings for the sensors based on SCPI Message Protocol
>> >> +--------------------------------------------------------------
>> >> +SCPI provides an API to access the various sensors on the SoC.
>> >> +
>> >> +Required properties:
>> >> +- compatible : should be "arm,scpi-sensors".
>> >> +- #thermal-sensor-cells: should be set to 1. This property follows the
>> >> +			 thermal device tree bindings[2].
>> >
>> > You need to specify what the valid values for this cell are.
>> 
>> The enumeration depends on the number of sensors exported by SCP
>> firmware - which is platform dependent. I could add add something like
>> if you think that is helpful -
>> 
>> "Valid cell value is a number between 0..n-1, where n is the number
>> of sensors exported by SCP firmware."
>
> Can the FW identifer space have holes? Or are they always contiguous?

The way the SCP interface is defined, the sensor identifiers are
contiguous, but not all are temperature sensors.

>
> If this is the same as the raw FW identifer value, specify that.
> Otherwise, you need to specify the mapping.

I'll update the patch to add mappings for Juno r0 (and r1 if I can get
my hands on one).

>
> There needs to be enough information for a dts author to figure out
> which values to place in the DT.

I understand. Except sometimes it is hard to get the firmware to commit to not
modify the ordering - discoverability and all that. :)

>
> Thanks,
> Mark.
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