Message-ID: <573E0758.3080109@ti.com>
Date:	Thu, 19 May 2016 13:35:04 -0500
From:	Dave Gerlach <d-gerlach@...com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Tony Lindgren <tony@...mide.com>,
	Mark Rutland <mark.rutland@....com>,
	Nishanth Menon <nm@...com>,
	Yegor Yefremov <yegorslists@...glemail.com>
Subject: Re: [PATCH 1/2] Documentation: dt: add bindings for ti-cpufreq

On 05/18/2016 10:15 PM, Viresh Kumar wrote:
> On 18-05-16, 18:30, Dave Gerlach wrote:
>> Add the device tree bindings document for the TI CPUFreq/OPP driver
>> on AM33xx and AM43xx SoCs. The operating-points-v2 binding allows us
>> to provide an opp-supported-hw property for each OPP to define when
>> it is available. This driver is responsible for reading and parsing
>> registers to determine which OPPs can be selectively enabled based
>> on the specific SoC in use by matching against the opp-supported-hw
>> data.
>
> Here and ...
>
>> Signed-off-by: Dave Gerlach <d-gerlach@...com>
>> ---
>>   .../devicetree/bindings/cpufreq/ti-cpufreq.txt     | 89 ++++++++++++++++++++++
>>   1 file changed, 89 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/cpufreq/ti-cpufreq.txt
>>
>> diff --git a/Documentation/devicetree/bindings/cpufreq/ti-cpufreq.txt b/Documentation/devicetree/bindings/cpufreq/ti-cpufreq.txt
>> new file mode 100644
>> index 000000000000..f719b2df2a1f
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/cpufreq/ti-cpufreq.txt
>> @@ -0,0 +1,89 @@
>> +Bindings for TI's CPUFreq driver
>> +================================
>> +
>> +The ti-cpufreq driver works with the operating-points-v2 binding described
>> +at [../opp/opp.txt] to make sure the proper OPPs for a platform get enabled
>> +and then creates a "cpufreq-dt" platform device to leverage the cpufreq-dt
>> +driver described in [cpufreq-dt.txt].
>> +
>> +Certain TI SoCs, like those in the am335x, am437x, am57xx, and dra7xx
>> +families support different OPPs depending on the silicon variant in use.
>> +The ti-cpufreq driver uses the revision and an efuse value from the SoC to
>> +provide the OPP framework with supported hardware information. This is used
>> +to determine which OPPs from the operating-points-v2 table get enabled. In
>> +order to maintain backwards compatilibity if this information is not present
>> +the "cpufreq-dt" platform device is still created to attempt to find an
>> +operating-points (v1) table, otherwise no OPPs will be available because
>> +safe OPPs cannot be determined.
>
> ... here..
>
> We shouldn't be talking about the drivers are going to use it, etc.
> This is a binding document, which should be independent of Linux
> kernel. It can be used by other Operating systems as well and so the
> implementation details should be just dropped.

Ah ok, will fix this up.

>
>> +
>> +Required properties:
>> +--------------------
>> +In 'cpus' nodes:
>> +- operating-points-v2: Phandle to the operating-points-v2 table to use
>> +- ti,syscon-efuse: Syscon phandle, offset to efuse register, efuse register
>> +		   mask, and efuse register shift to get the relevant bits
>> +		   that describe OPP availability
>> +- ti,syscon-rev: Syscon and offset used to look up revision value on SoC
>
> These are proper sentences and so maybe a full-stop (.) at the end of
> each line ?

Sure, can do this.

>
>> +
>> +In 'operating-points-v2' table:
>> +- opp-supported-hw: Two bitfields indicating:
>> +	1. Which revision of the SoC the OPP is supported by
>> +	2. Which eFuse bits indicate this OPP is available
>> +
>> +	A bitwise and is performed against these values and if any bit
>
>                    AND or &

Ok will change.

>
>> +	matches, the OPP gets enabled.
>> +
>> +NOTE: Without the above, platform-device for "cpufreq-dt" is still created
>> +      but no determination of which OPPs should be available is done, but this
>> +      allows for use of a v1 operating-points table.
>
> Again, these are implementation details.. should be dropped.

Yes, will do.

>
>> +
>> +Example:
>> +--------
>> +
>> +/* From arch/arm/boot/dts/am4372.dtsi */
>> +cpus {
>> +	cpu: cpu@0 {
>> +		...
>> +
>> +		operating-points-v2 = <&cpu0_opp_table>;
>> +
>> +		ti,syscon-efuse = <&scm_conf 0x610 0x3f 0>;
>> +		ti,syscon-rev = <&scm_conf 0x600>;
>
> @Rob: Can we add properties to the CPU node just like that ?
>
>> +
>> +		...
>> +	};
>> +};
>> +
>> +cpu0_opp_table: opp_table0 {
>> +	compatible = "operating-points-v2";
>
> Otherwise, you could have added above properties right here and added
> your own compatible string..

I felt they went well with the cpu node but thinking about it more they 
fit just as well here, I'd be fine moving them.

>
>> +	opp50@...000000 {
>> +		opp-hz = /bits/ 64 <300000000>;
>> +		opp-microvolt = <950000>;
>> +		opp-supported-hw = <0xFF 0x01>;
>> +		opp-suspend;
>> +	};
>> +
>> +	opp100@...000000 {
>> +		opp-hz = /bits/ 64 <600000000>;
>> +		opp-microvolt = <1100000>;
>> +		opp-supported-hw = <0xFF 0x04>;
>> +	};
>> +
>> +	opp120@...000000 {
>> +		opp-hz = /bits/ 64 <720000000>;
>> +		opp-microvolt = <1200000>;
>> +		opp-supported-hw = <0xFF 0x08>;
>> +	};
>> +
>> +	oppturbo@...000000 {
>> +		opp-hz = /bits/ 64 <800000000>;
>> +		opp-microvolt = <1260000>;
>> +		opp-supported-hw = <0xFF 0x10>;
>> +	};
>> +
>> +	oppnitro@...0000000 {
>> +		opp-hz = /bits/ 64 <1000000000>;
>> +		opp-microvolt = <1325000>;
>> +		opp-supported-hw = <0xFF 0x20>;
>
> so the first one is always FF ? Why have it then ?

Hmmm, this particular platform was a bad choice for the example, I will 
use a different platform that makes use of the first field better. This 
platform supports all OPPs on all revisions, but am335x does not so I 
will use that instead in v2.

Regards,
Dave

>
>> +	};
>> +};
>

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