linux-kernel - Re: [PATCH V1 Resend 2/3] cpufreq: dt: Add generic platform-device creation support

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Date:	Fri, 1 Apr 2016 09:15:09 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <rob.herring@...aro.org>,
	Krzysztof Kozłowski <k.kozlowski@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Heiko Stübner <heiko@...ech.de>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Matthew McClintock <mmcclint@...eaurora.org>,
	xf@...k-chips.com, Rafael Wysocki <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH V1 Resend 2/3] cpufreq: dt: Add generic platform-device
 creation support

On Fri, Apr 1, 2016 at 5:23 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> Cc'ing Rob and Mason.
>
> On 30-03-16, 09:53, Arnd Bergmann wrote:
>> I think it should be something in the /cpus or the /opp_table hierarchy,
>> not the root of the device tree, but other than that I don't care much
>> whether it's a variation of the oppv2 compatible string or an additional
>> property in any of the nodes.
>
> So you mean for future DT files we can have something like this:
>
>         cpus {
>                 compatible = "operation-points-v2";
>                 #address-cells = <1>;
>                 #size-cells = <0>;
>
>                 cpu@0 {
>                         compatible = "arm,cortex-a9";
>                         reg = <0>;
>                         next-level-cache = <&L2>;
>                         operating-points-v2 = <&cpu0_opp_table>;
>                 };
>         };
>
>         cpu0_opp_table: opp_table0 {
>                 opp@...0000000 {
>                         opp-hz = /bits/ 64 <1000000000>;
>                         opp-microvolt = <970000 975000 985000>;
>                         opp-microamp = <70000>;
>                         clock-latency-ns = <300000>;
>                         opp-suspend;
>                 };
>                 opp@...0000000 {
>                         opp-hz = /bits/ 64 <1100000000>;
>                         opp-microvolt = <980000 1000000 1010000>;
>                         opp-microamp = <80000>;
>                         clock-latency-ns = <310000>;
>                 };
>         };
> };
>
>
> And the cpufreq-dt driver can match /cpus node's compatible string against
> "operating-points-v2" and create a device at runtime ?
>
> @Rob: Will that be acceptable to you? We are discussing (again) about how to
> probe cpufreq-dt driver automatically for platforms :)

No, I don't think that belongs in /cpus.

Part of the problem is this requires a DT change if you switch between
a platform-specific driver and generic driver.

I don't understand the issue having a little bit of code to parse the
DT and create the device. If you are worried about having a long list
of platforms, you could instead check the tree for operating-points-v2
property in the cpu node and create the device unless the platform is
black-listed.

Rob