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

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Message-ID: <20160407083036.GB3201@vireshk-i7>
Date:	Thu, 7 Apr 2016 14:00:36 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Rob Herring <robherring2@...il.com>
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 01-04-16, 09:15, Rob Herring wrote:
> On Fri, Apr 1, 2016 at 5:23 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > 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.

Right.

> I don't understand the issue having a little bit of code to parse the
> DT and create the device.

I am fine with that, we were just re-evaluating our options :)

> If you are worried about having a long list
> of platforms,

At least I am not.

> 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.

I don't really like the black-list idea much. It forces a Non
cpufreq-dt platform to edit cpufreq-dt related file, just to make its
own cpufreq driver work.

I find that ugly somehow :)

-- 
viresh