linux-kernel - Re: [PATCH v4 1/3] dt-bindings: interconnect: imx8m-noc: Add fsl,icc-id property

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Message-ID: <YgVoRols6AA5HAze@abelvesa>
Date:   Thu, 10 Feb 2022 21:32:22 +0200
From:   Abel Vesa <abel.vesa@....com>
To:     Rob Herring <robh@...nel.org>
Cc:     Georgi Djakov <djakov@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 1/3] dt-bindings: interconnect: imx8m-noc: Add
 fsl,icc-id property

On 22-01-21 15:27:08, Rob Herring wrote:
> On Thu, Jan 06, 2022 at 06:41:48PM +0200, Abel Vesa wrote:
> > Add documentation for fsl,icc-id property.
> > 
> > Signed-off-by: Abel Vesa <abel.vesa@....com>
> > ---
> > 
> > Changes since v3:
> >  * fixed typo in property description
> > 
> >  .../devicetree/bindings/interconnect/fsl,imx8m-noc.yaml      | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/interconnect/fsl,imx8m-noc.yaml b/Documentation/devicetree/bindings/interconnect/fsl,imx8m-noc.yaml
> > index b8204ed22dd5..dc7f6b6f508a 100644
> > --- a/Documentation/devicetree/bindings/interconnect/fsl,imx8m-noc.yaml
> > +++ b/Documentation/devicetree/bindings/interconnect/fsl,imx8m-noc.yaml
> > @@ -47,6 +47,11 @@ properties:
> >    operating-points-v2: true
> >    opp-table: true
> >  
> > +  fsl,icc-id:
> > +    $ref: "/schemas/types.yaml#/definitions/uint32"
> > +    description:
> > +      unique ID used for linking i.MX bus or ddrc node to interconnect
> 
> Where does this unique ID come from and how is it used? Why aren't cells 
> in 'interconnects' sufficient for this?

Sorry for the late reply.

Well, the 'inteconnects' property is documented as a pair of
interconnect nodes, specifically source and destination (endpoints).

The fsl,icc-id is used here to allow the the imx-bus and imx8m-ddrc
nodes to specify which icc node it belongs to.

Basically, the 'interconnects' property is used by an icc consumer
to specify a path towards the target, while the fsl,icc-id is used
here to specify which icc node (in this case, not an endpoint)
belongs to which imx-bus or imx8m-ddrc device.

> 
> > +
> >    fsl,ddrc:
> >      $ref: "/schemas/types.yaml#/definitions/phandle"
> >      description:
> > -- 
> > 2.31.1
> > 
> >