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

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Date:   Wed, 13 Jun 2018 07:57:47 -0600
From:   Rob Herring <robh@...nel.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Matt Sealey <Matt.Sealey@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "mathieu.poirier@...aro.org" <mathieu.poirier@...aro.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

On Wed, Jun 13, 2018 at 7:35 AM, Suzuki K Poulose
<Suzuki.Poulose@....com> wrote:
> Hi Matt,
>
> Thanks for your comments, responses inline.
>
> On 13/06/18 13:49, Matt Sealey wrote:
>>
>> Suzuki,
>>
>> Why not use “unit”?
>>
>> I believe we had this discussion years ago about numbering serial ports
>> and sdhci (i.e. how do you know it’s UART0 or UART1 from just the address?
>> Some SoC’s don’t address sequentially *or* in a forward direction) - I
>> believe it’s not exactly codified in ePAPR, not am I sure where it may be
>> otherwise, but it exists.
>
>
> We have different situation here. We need to know *the port number* as
> understood by the
> hardware, so that we can enable *the specific* port for a given path.
>
>>
>> I agree with Rob on the slave-mode nonsense, this is an SPI controller
>> concept weirdly stuffed into a directed graph which implicitly tells you the
>> data direction - it’s a rooted tree (just like DT!).

OF graph is not directional. All links must be bi-directional and in
fact dtc checks that now. The parent node should know the numbering
and direction of each port.

> Btw, the "slave-mode" is not a standard DT graph binding. It is not part of
> the
> generic DT graph binding. In fact the generic bindings stay away from the
> direction
> aspect and explicitly mentions the same.

I really don't like slave-mode nor coresight,hwid.

I would prefer to see getting rid of both and splitting ports into
"in-ports" and "out-ports" nodes instead of a single "ports" node.
Then you don't need any of these properties and reg can be used as the
hwid.

Rob