linux-kernel - Re: [PATCH v5 3/7] ARM: dts: Exynos542x/5800: add CPU OPP properties

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Date:	Fri, 11 Dec 2015 13:53:26 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Rob Herring <robh+dt@...nel.org>
Cc:	Javier Martinez Canillas <javier@....samsung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Thomas Abraham <thomas.ab@...sung.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Mike Turquette <mturquette@...libre.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	Ben Gamari <ben@...rt-cactus.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Lukasz Majewski <l.majewski@...sung.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Kevin Hilman <khilman@...aro.org>,
	Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>,
	Anand Moon <linux.amoon@...il.com>,
	linux-samsung-soc@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	Andreas Faerber <afaerber@...e.de>
Subject: Re: [PATCH v5 3/7] ARM: dts: Exynos542x/5800: add CPU OPP properties

On 11.12.2015 13:38, Viresh Kumar wrote:
> On 11-12-15, 13:18, Krzysztof Kozlowski wrote:
>> We had such configuration before (before df09df6f9ac3). I don't see any
>> benefit in what you described. Where is the "thing" to be fixed? It is
>> mixed up. The contiguous ordering is easier to read and more natural.
> 
> This is what you are doing today (keeping on one CPU per cluster to
> simplify it):
> 
> 		cpu0: cpu@0 {
> 			device_type = "cpu";
> 			compatible = "arm,cortex-a15";
> 			reg = <0x0>;
> 			clock-frequency = <1800000000>;
> 			cci-control-port = <&cci_control1>;
> 		};
> 
> 		cpu4: cpu@100 {
> 			device_type = "cpu";
> 			compatible = "arm,cortex-a7";
> 			reg = <0x100>;
> 			clock-frequency = <1000000000>;
> 			cci-control-port = <&cci_control0>;
> 		};
> 
> 
> Then you overwrite it with:
> 
>                 &cpu0 {
>                 	device_type = "cpu";
>                 	compatible = "arm,cortex-a7";
>                 	reg = <0x100>;
>                 	clock-frequency = <1000000000>;
>                 	cci-control-port = <&cci_control0>;
>                 };
>                 
>                 &cpu4 {
>                 	device_type = "cpu";
>                 	compatible = "arm,cortex-a15";
>                 	reg = <0x0>;
>                 	clock-frequency = <1800000000>;
>                 	cci-control-port = <&cci_control1>;
>                 };
> 
> 
> Don't you think this isn't the right way of solving problems?
> 
> The DT overwrite feature isn't there to do such kind of stuff, though
> it doesn't stop you from doing that.

This is quite ugly, indeed, and it is getting uglier :)... but it does
not violate the idea of DT to describe the hardware. Both hardware
descriptions - the 5420 and overridden - are entirely correct... because
the CPU ordering comes from booting sequence (actually code in IROM
decides according to pulled up GPIO gpg2-1).


> Either you should keep separate paths for both the SoCs,

I like that idea. That makes it much more readable. Thanks for feedback!
I will send a patch for that.


> or can solve
> it the way I suggested earlier.
> 
> This came up because in the current series you are doing this:
> 
> 		cpu0: cpu@0 {
> 			compatible = "arm,cortex-a15";
>                         operating-points-v2 = <&cpu0_opp_table>;
> 		};
> 
> 		cpu4: cpu@100 {
> 			device_type = "cpu";
> 			compatible = "arm,cortex-a7";
>                         operating-points-v2 = <&cpu1_opp_table>;
> 		};
> 
> 
> Then you overwrite it with:
> 
>                 &cpu0 {
>                 	compatible = "arm,cortex-a7";
>                         operating-points-v2 = <&cpu1_opp_table>;
>                 };
>                 
>                 &cpu4 {
>                 	compatible = "arm,cortex-a15";
>                         operating-points-v2 = <&cpu0_opp_table>;
>                 };

Yes, it is getting uglier with each change...

Best regards,
Krzysztof


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