linux-kernel - Re: [PATCH 1/2] Documentation: dt: add bindings for ti-cpufreq

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Message-ID: <20160519031559.GK24777@vireshk-i7>
Date:	Thu, 19 May 2016 08:45:59 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Dave Gerlach <d-gerlach@...com>
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 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.

> +
> +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 ?

> +
> +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 &

> +	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.

> +
> +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..

> +	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 ?

> +	};
> +};

-- 
viresh