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

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Date:	Mon, 14 Sep 2015 16:15:40 +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 04:01:09PM +0100, Punit Agrawal wrote:
> 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.

Ok. That's fine by me; I was confused and thought that there was some
internal mapping.

> >> > 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.

That's fine by me. The important part is that the value is a raw Sensor
ID as the FW uses. So long as we state that, the IDs themselves can come
from whatever documentation is valid for a particular instance.

Thanks for the info!

Thanks,
Mark.
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