linux-kernel - Re: [PATCH 3/6] dt-bindings: serdev: ngsm: Add binding for GNSS child node

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Message-ID: <20200528095151.GE10358@localhost>
Date:   Thu, 28 May 2020 11:51:51 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Tony Lindgren <tony@...mide.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johan Hovold <johan@...nel.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Lee Jones <lee.jones@...aro.org>, Jiri Slaby <jslaby@...e.cz>,
        Merlijn Wajer <merlijn@...zup.org>,
        Pavel Machek <pavel@....cz>,
        Peter Hurley <peter@...leysoftware.com>,
        Sebastian Reichel <sre@...nel.org>,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH 3/6] dt-bindings: serdev: ngsm: Add binding for GNSS
 child node

On Wed, May 27, 2020 at 01:28:17PM -0600, Rob Herring wrote:
> On Tue, May 12, 2020 at 02:47:10PM -0700, Tony Lindgren wrote:
> > For motorola modem case, we may have a GNSS device on channel 4.
> > Let's add that to the binding and example.
> > 
> > Signed-off-by: Tony Lindgren <tony@...mide.com>
> > ---
> >  .../devicetree/bindings/serdev/serdev-ngsm.yaml          | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/serdev/serdev-ngsm.yaml b/Documentation/devicetree/bindings/serdev/serdev-ngsm.yaml
> > --- a/Documentation/devicetree/bindings/serdev/serdev-ngsm.yaml
> > +++ b/Documentation/devicetree/bindings/serdev/serdev-ngsm.yaml
> > @@ -42,6 +42,10 @@ allOf:
> >            description: Name of the USB PHY
> >            const: usb
> >  
> > +        compatible:
> > +          description: GNSS receiver
> > +          const: motorola,mapphone-mdm6600-gnss
> 
> I'm not sure how this isn't failing on the example because it is wrong.
> 
> You're saying this compatible belongs at the same level as 
> phys/phy-names, but that would be the parent which already has a 
> compatible. You have to define a child node property (gnss@4) and have 
> 'compatible' under it. At that point, this schema becomes very much 
> Motorola specific.
> 
> > +
> >        required:
> >          - phys
> >          - phy-names
> > @@ -61,4 +65,9 @@ examples:
> >        phy-names = "usb";
> >        #address-cells = <1>;
> >        #size-cells = <0>;
> > +
> > +      gnss@4 {
> > +         compatible = "motorola,mapphone-mdm6600-gnss";
> > +         reg = <4>;
> > +      };
> >      };
> > -- 
> > 2.26.2

And since we're describing a mux, I think you need nodes for the virtual
ports rather than a reg property in what should be a serial client. That
is something like

	serial@nnn {
		modem {
			compatible = "etsi,ts27001-mux";

			serial@4 {
				compatible = "etsi,ts27001-serial";
				reg = <4>;

				gnss {
					compatible = "motorola,motmdm-gnss";
				};
			};
		};
	};

This way you can actually use serdev for the client drivers (e.g. for
gnss), and those drivers also be used for non-muxed ports if needed
(e.g. over USB).

Johan