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Date:   Mon, 18 Sep 2023 09:42:39 +0200
From:   Herve Codina <herve.codina@bootlin.com>
To:     Conor Dooley <conor@kernel.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>, Lee Jones <lee@kernel.org>,
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        Christophe Leroy <christophe.leroy@csgroup.eu>,
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        Simon Horman <horms@kernel.org>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v5 08/31] dt-bindings: soc: fsl: cpm_qe: cpm1-scc-qmc:
 Add support for QMC HDLC
Message-ID: <20230918094239.4d2d0c32@bootlin.com>
In-Reply-To: <20230913-unburned-overturn-41b83e1eed25@spud>
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        <20230913-unburned-overturn-41b83e1eed25@spud>
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Hi Conor,

On Wed, 13 Sep 2023 15:59:41 +0100
Conor Dooley <conor@kernel.org> wrote:

> On Wed, Sep 13, 2023 at 03:56:16PM +0100, Conor Dooley wrote:
> > On Wed, Sep 13, 2023 at 04:52:50PM +0200, Herve Codina wrote:  
> > > On Wed, 13 Sep 2023 15:42:45 +0100
> > > Conor Dooley <conor@kernel.org> wrote:
> > >   
> > > > On Wed, Sep 13, 2023 at 09:26:40AM +0200, Herve Codina wrote:  
> > > > > Hi Conor,
> > > > > 
> > > > > On Tue, 12 Sep 2023 18:21:58 +0100
> > > > > Conor Dooley <conor@kernel.org> wrote:
> > > > >     
> > > > > > On Tue, Sep 12, 2023 at 12:10:18PM +0200, Herve Codina wrote:    
> > > > > > > The QMC (QUICC mutichannel controller) is a controller present in some
> > > > > > > PowerQUICC SoC such as MPC885.
> > > > > > > The QMC HDLC uses the QMC controller to transfer HDLC data.
> > > > > > > 
> > > > > > > Additionally, a framer can be connected to the QMC HDLC.
> > > > > > > If present, this framer is the interface between the TDM bus used by the
> > > > > > > QMC HDLC and the E1/T1 line.
> > > > > > > The QMC HDLC can use this framer to get information about the E1/T1 line
> > > > > > > and configure the E1/T1 line.
> > > > > > > 
> > > > > > > Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> > > > > > > ---
> > > > > > >  .../bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml   | 13 +++++++++++++
> > > > > > >  1 file changed, 13 insertions(+)
> > > > > > > 
> > > > > > > diff --git a/Documentation/devicetree/bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml b/Documentation/devicetree/bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml
> > > > > > > index 82d9beb48e00..b5073531f3f1 100644
> > > > > > > --- a/Documentation/devicetree/bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml
> > > > > > > +++ b/Documentation/devicetree/bindings/soc/fsl/cpm_qe/fsl,cpm1-scc-qmc.yaml
> > > > > > > @@ -101,6 +101,16 @@ patternProperties:
> > > > > > >            Channel assigned Rx time-slots within the Rx time-slots routed by the
> > > > > > >            TSA to this cell.
> > > > > > >  
> > > > > > > +      compatible:
> > > > > > > +        const: fsl,qmc-hdlc
> > > > > > > +
> > > > > > > +      fsl,framer:
> > > > > > > +        $ref: /schemas/types.yaml#/definitions/phandle
> > > > > > > +        description:
> > > > > > > +          phandle to the framer node. The framer is in charge of an E1/T1 line
> > > > > > > +          interface connected to the TDM bus. It can be used to get the E1/T1 line
> > > > > > > +          status such as link up/down.      
> > > > > > 
> > > > > > Sounds like this fsl,framer property should depend on the compatible
> > > > > > being present, no?    
> > > > > 
> > > > > Well from the implementation point of view, only the QMC HDLC driver uses this
> > > > > property.
> > > > > 
> > > > > From the hardware description point of view, this property means that the time slots
> > > > > handled by this channel are connected to the framer. So I think it makes sense for
> > > > > any channel no matter the compatible (even if compatible is not present).
> > > > > 
> > > > > Should I change and constraint the fsl,framer property to the compatible presence ?
> > > > > If so, is the following correct for this contraint ?
> > > > >    --- 8< ---
> > > > >    dependencies:
> > > > >      - fsl,framer: [ compatible ];
> > > > >    --- 8< ---    
> > > > 
> > > > The regular sort of
> > > > if:
> > > > 	compatible:
> > > > 		contains:
> > > > 			const: foo
> > > > then:
> > > > 	required:
> > > > 		- fsl,framer
> > > > would fit the bill, no?  
> > > 
> > > Not sure.
> > > "fsl,framer" is an optional property (depending on the hardware we can have
> > > a framer or not).  
> > 
> > Ah apologies, I had it backwards! Your suggestion seems fair in that
> > case.  
> 
> Or actually,
> if:
> 	compatible:
> 		not:
> 	 		contains:
> 	 			const: foo
>  then:
>  	properties:
>  		fsl,framer: false
> ? That should do the trick in a more conventional way.

Thanks for this proposal.
I will use it in the next iteration.

Regards,
Hervé