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

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Date:	Mon, 14 Sep 2015 15:43:30 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Punit Agrawal <punit.agrawal@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	"edubezval@...il.com" <edubezval@...il.com>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH v3 1/5] Documentation: add DT bindings for ARM SCPI
 sensors

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?

> > 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.

> > 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.

Thanks,
Mark.
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