linux-kernel - Re: [PATCH RFC v6 1/6] dt-bindings: exynos-bus: Add documentation for interconnect properties

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Message-ID: <35d9d396-b553-a815-1f3b-1af4dc37a2ca@samsung.com>
Date:   Fri, 28 Aug 2020 16:49:33 +0200
From:   Sylwester Nawrocki <s.nawrocki@...sung.com>
To:     Rob Herring <robh@...nel.org>, georgi.djakov@...aro.org
Cc:     cw00.choi@...sung.com, krzk@...nel.org, devicetree@...r.kernel.org,
        a.swigon@...sung.com, myungjoo.ham@...sung.com,
        inki.dae@...sung.com, sw0312.kim@...sung.com,
        b.zolnierkie@...sung.com, m.szyprowski@...sung.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC v6 1/6] dt-bindings: exynos-bus: Add documentation
 for interconnect properties

On 30.07.2020 14:28, Sylwester Nawrocki wrote:
> On 09.07.2020 23:04, Rob Herring wrote:
>> On Thu, Jul 02, 2020 at 06:37:19PM +0200, Sylwester Nawrocki wrote:
>>> Add documentation for new optional properties in the exynos bus nodes:
>>> samsung,interconnect-parent, #interconnect-cells, bus-width.
>>> These properties allow to specify the SoC interconnect structure which
>>> then allows the interconnect consumer devices to request specific
>>> bandwidth requirements.
>>>
>>> Signed-off-by: Artur Świgoń <a.swigon@...sung.com>
>>> Signed-off-by: Sylwester Nawrocki <s.nawrocki@...sung.com>

>>> --- a/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>>> +++ b/Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>>> @@ -51,6 +51,13 @@ Optional properties only for parent bus device:
>>>  - exynos,saturation-ratio: the percentage value which is used to calibrate
>>>  			the performance count against total cycle count.
>>>  
>>> +Optional properties for interconnect functionality (QoS frequency constraints):
>>> +- samsung,interconnect-parent: phandle to the parent interconnect node; for
>>> +  passive devices should point to same node as the exynos,parent-bus property.

>> Adding vendor specific properties for a common binding defeats the 
>> point.

Actually we could do without any new property if we used existing interconnect
consumers binding to specify linking between the provider nodes. I think those
exynos-bus nodes could well be considered both the interconnect providers 
and consumers. The example would then be something along the lines 
(yes, I know the bus node naming needs to be fixed):

	soc {
		bus_dmc: bus_dmc {
			compatible = "samsung,exynos-bus";
			/* ... */
			samsung,data-clock-ratio = <4>;
			#interconnect-cells = <0>;
		};

		bus_leftbus: bus_leftbus {
			compatible = "samsung,exynos-bus";
			/* ... */
			interconnects = <&bus_leftbus &bus_dmc>;
			#interconnect-cells = <0>;
		};

		bus_display: bus_display {
			compatible = "samsung,exynos-bus";
			/* ... */
			interconnects = <&bus_display &bus_leftbus>;
			#interconnect-cells = <0>;
		};


		&mixer {
			compatible = "samsung,exynos4212-mixer";
			interconnects = <&bus_display &bus_dmc>;
			/* ... */
		};
	};

What do you think, Georgi, Rob?

-- 
Regards
Sylwester