linux-kernel - Re: [PATCH 00/20] coresight: Update device tree bindings

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Date:   Wed, 20 Jun 2018 10:53:26 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org, xuwei5@...ilicon.com,
        lipengcheng8@...wei.com, orsonzhai@...il.com, zhang.lyra@...il.com,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        "Ivan T . Ivanov" <ivan.ivanov@...aro.org>,
        Stefan Agner <stefan@...er.ch>, shawnguo@...nel.org,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Liviu Dudau <liviu.dudau@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     mathieu.poirier@...aro.org, robh@...nel.org,
        frowand.list@...il.com, mark.rutland@....com, sudeep.holla@....com,
        arm@...nel.org, linux-kernel@...r.kernel.org, matt.sealey@....com,
        john.horley@....com, charles.garcia-tobin@....com,
        coresight@...ts.linaro.org, devicetree@...r.kernel.org,
        mike.leach@...aro.org
Subject: Re: [PATCH 00/20] coresight: Update device tree bindings

On 05/06/18 22:43, Suzuki K Poulose wrote:
> Coresight uses DT graph bindings to describe the connections of the
> components. However we have some undocumented usage of the bindings
> to describe some of the properties of the connections.
> 
> The coresight driver needs to know the hardware ports invovled
> in the connection and the direction of data flow to effectively
> manage the trace sessions. So far we have relied on the "port"
> address (as described by the generic graph bindings) to represent
> the hardware port of the component for a connection.
> 

...

> There were three options considered for the hardware port number scheme:
> 


...

>   3) Use explicit properties (implemented in the series) for the hardware
>      port id and direction. We define a new property "coresight,hwid" for
>      each endpoint in coresight devices to specify the hardware port number
>      explicitly. Also use a separate property "direction" to specify the
>      direction of the data flow.
> 
> 	e.g,
> 
> 	port@0{
> 		reg = <0>;
> 		endpoint {
> 			direction = <1>;	// Output
> 			coresight,hwid = <0>;	// Port # 0
> 		}
> 	};
> 
> 	port@1{
> 		reg = <1>;
> 		endpoint {
> 			direction = <0>;	// Input
> 			coresight,hwid = <0>;	// Port # 0
> 		};
> 	};
> 
>      Pros:
>         - The bindings are formal and reader friendly, and less prone to errors.
>      Cons:
>         - Backward compatibility is lost.
> 
> 
> This series implements Option (3) listed above and falls back to the old
> bindings if the new bindings are not available. This allows the systems
> with old bindings work with the new driver. The driver now issues a warning
> (once) when it encounters the old bindings.

  ....

>    dts: juno: Update coresight bindings for hw port
>    dts: hisilicon: Update coresight bindings for hw ports
>    dts: spreadtrum: Update coresight bindings for hw ports
>    dts: qcom: Update coresight bindings for hw ports
>    dts: arm: hisilicon: Update coresight bindings for hardware port
>    dts: arm: imx7{d,s}: Update coresight binding for hardware ports
>    dts: arm: omap: Update coresight bindings for hardware ports
>    dts: arm: qcom: Update coresight bindings for hardware ports
>    dts: sama5d2: Update coresight bindings for hardware ports
>    dts: ste-dbx5x0: Update coresight bindings for hardware port
>    dts: tc2: Update coresight bindings for hardware ports
> 

All,

Pleas hold on with applying the DTS changes listed above. There are
still some on going discussions on the bindings and we are yet to
come to a conclusion [0]. And there are high chances that these might
change. Sorry for the inconvenience.

[0] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-June/582269.html

Kind regards
Suzuki