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

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Message-ID: <9hhfv2hdozu.fsf@e105922-lin.cambridge.arm.com>
Date:	Mon, 14 Sep 2015 16:01:09 +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:

> On Mon, Sep 14, 2015 at 03:38:36PM +0100, Punit Agrawal wrote:
>> 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.
>
> Ok. So how exactly are they enumerated for this binding?

The sensor enumeration for r0 (which I've verified) and r1 can be found
at [0]. The valid cell values are identifiers for the 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).
>
> If there's identical logic mapping the two, we might just be able to
> describe that rather than having to add tables all the time.
>

After seeing the mapping already published, I am wondering if there is
any value in duplicating the information. If there are no objections,
I'll update this patch to add pointers instead.

>> > 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. :)
>
> If they do that, then things are broken regardless, no? I guess that'll
> be clear if/when I see how the mapping works.

[0] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0922b/apas03s22.html

>
> Thanks,
> Mark.
> --
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