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Date: Mon, 26 Feb 2024 11:56:16 +0000
From: Conor Dooley <conor.dooley@microchip.com>
To: =?iso-8859-1?Q?Th=E9o?= Lebrun <theo.lebrun@bootlin.com>
CC: Conor Dooley <conor@kernel.org>, Greg Kroah-Hartman
	<gregkh@linuxfoundation.org>, Rob Herring <robh+dt@kernel.org>, Krzysztof
 Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley
	<conor+dt@kernel.org>, Roger Quadros <rogerq@kernel.org>, Peter Chen
	<peter.chen@kernel.org>, Pawel Laszczak <pawell@cadence.com>, Nishanth Menon
	<nm@ti.com>, Vignesh Raghavendra <vigneshr@ti.com>, Tero Kristo
	<kristo@kernel.org>, Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	=?iso-8859-1?Q?Gr=E9gory?= Clement <gregory.clement@bootlin.com>, Kevin
 Hilman <khilman@kernel.org>, Alan Stern <stern@rowland.harvard.edu>,
	<linux-usb@vger.kernel.org>, <devicetree@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 1/8] dt-bindings: usb: ti,j721e-usb: drop useless
 compatible list
Message-ID: <20240226-portable-rockslide-e501667a0d9a@wendy>
References: <20240223-j7200-usb-suspend-v3-0-b41c9893a130@bootlin.com>
 <20240223-j7200-usb-suspend-v3-1-b41c9893a130@bootlin.com>
 <20240223-clarity-variably-206b01b7276a@spud>
 <CZEXXXQDZZWB.1M5CTZAFVO4YP@bootlin.com>
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On Mon, Feb 26, 2024 at 11:33:06AM +0100, Th=E9o Lebrun wrote:
> Hello Conor,
>=20
> On Fri Feb 23, 2024 at 7:12 PM CET, Conor Dooley wrote:
> > On Fri, Feb 23, 2024 at 05:05:25PM +0100, Th=E9o Lebrun wrote:
> > > Compatible can be A or B, not A or B or A+B. Remove last option.
> > > A=3Dti,j721e-usb and B=3Dti,am64-usb.
> > >=20
> > > Signed-off-by: Th=E9o Lebrun <theo.lebrun@bootlin.com>
> > > ---
> > >  Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml | 9 +++------
> > >  1 file changed, 3 insertions(+), 6 deletions(-)
> > >=20
> > > diff --git a/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml =
b/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml
> > > index 95ff9791baea..949f45eb45c2 100644
> > > --- a/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml
> > > +++ b/Documentation/devicetree/bindings/usb/ti,j721e-usb.yaml
> > > @@ -11,12 +11,9 @@ maintainers:
> > > =20
> > >  properties:
> > >    compatible:
> > > -    oneOf:
> > > -      - const: ti,j721e-usb
> > > -      - const: ti,am64-usb
> > > -      - items:
> > > -          - const: ti,j721e-usb
> > > -          - const: ti,am64-usb
> >
> > Correct, this makes no sense. The devices seem to be compatible though,
> > so I would expect this to actually be:
> > oneOf:
> >   - const: ti,j721e-usb
> >   - items:
> >       - const: ti,am64-usb
> >       - const: ti,j721e-usb
>=20
> I need your help to grasp what that change is supposed to express? Would
> you mind turning it into english sentences?
> A=3Dti,j721e-usb and B=3Dti,am64-usb. My understanding of your proposal is
> that a device can either be compat with A or B. But B is compatible
> with A so you express it as a list of items. If B is compat with A then
> A is compat with B. Does the order of items matter?

The two devices are compatible with each other, based on an inspection of
the driver and the existing "A+B" setup. If this was a newly submitted
binding, "B" would not get approved because "A+B" allows support without
software changes and all that jazz.

Your patch says that allowing "A", "B" and "A+B" makes no sense and you
suggest removing "A+B". I am agreeing that it makes no sense to allow
all 3 of these situations.

What I also noticed is other problems with the binding. What should have
been "A+B" is actually documented as "B+A", but that doesn't make sense
when the originally supported device is "A".

Therefore my suggestion was to only allow "A" and "A+B", which is what
we would (hopefully) tell you to do were you submitting the am64 support
as a new patch today.

> I've not applied your proposal to check for dtbs_check but I'd guess it
> would throw warnings for the single existing upstream DTSI (as of
> v6.8-rc6) that uses "ti,am64-usb"? See:
> arch/arm64/boot/dts/ti/k3-am64-main.dtsi.

Yeah, it would but it's not as if that cannot be changed. There's no
concerns here about backwards compatibility here, right?

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