linux-kernel - Re: [RFC PATCH 6/8] dts: coresight: Clean up the device tree graph bindings

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Date:   Tue, 3 Jul 2018 10:44:13 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Rob Herring <robh@...nel.org>
Cc:     Matt Sealey <Matt.Sealey@....com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sudeep Holla <Sudeep.Holla@....com>,
        Mark Rutland <Mark.Rutland@....com>,
        "frowand.list@...il.com" <frowand.list@...il.com>,
        Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
        John Horley <John.Horley@....com>,
        "mike.leach@...aro.org" <mike.leach@...aro.org>,
        "coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RFC PATCH 6/8] dts: coresight: Clean up the device tree graph
 bindings

Hi Rob,

On 14/06/18 14:59, Rob Herring wrote:
> On Thu, Jun 14, 2018 at 2:53 AM, Suzuki K Poulose
> <Suzuki.Poulose@....com> wrote:
>> On 13/06/18 22:07, Matt Sealey wrote:
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: Mathieu Poirier <mathieu.poirier@...aro.org>
>>>>
>>>>> So, if the suggestion is to use an existing property "unit", I am fine
>>>>> with it, if people agree to it.
>>>>
>>>>
>>>> If we're going to have something sharply different than ACPI I prefer
>>>> Rob's idea.
>>
>>
>> No, the above comment is about using "unit" ( if it is a standard property
>> for specifying something specific to hardware) instead of "coresight,hwid".
>> I would prefer to stick to the DT graph bindings, because :
> 
> "unit" is not a standard property and I don't like it either.
> 
>>
>> 1) The connections are bi-directional => Well, not necessarily
>> bi-directional
>> in terms of the data flow. But the connection information is critical. i.e,
>> we need information about both the end-points of a connection, which the DT
>> graph bindings solves.
>>
>> All we are missing is a way for specifying the "hardware port" number and
>> the
>> direction of flow. I don't see why do we need to create something new just
>> for
>> these two properties for something that exists today and works reasonably
>> well
>> for the usecase.
> 
> If you have "in-ports" and "out-ports" nodes, then that gives you
> direction and you can use reg for the "hardware port".
> 
> in-ports {
>    port@0 {
>      reg = <0>;
>      endpoint {...};
>    };
>    port@1 {
>      reg = <1>;
>      endpoint {...};
>    };
> };
> out-ports {
>    port@0 {
>      reg = <0>;
>      endpoint {...};
>    };
> };
> 
> I'll need to check, but dtc may need an update to not warn about this.
> 

I did a quick check with the upstream dtc tool and the above form is
doesn't generate any errors.

Mathieu, Rob,

Shall I proceed with the proposal above ?


Suzuki