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Date: Tue, 27 Feb 2024 08:07:02 +0000
From: Conor Dooley <conor.dooley@microchip.com>
To: Vignesh Raghavendra <vigneshr@ti.com>
CC: =?iso-8859-1?Q?Th=E9o?= Lebrun <theo.lebrun@bootlin.com>, 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>, 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: <20240227-radiated-fame-57a2e685f1b0@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>
 <20240226-portable-rockslide-e501667a0d9a@wendy>
 <CZF33W51MC4M.3GUBZFQXT39DB@bootlin.com>
 <37ab0886-0cd1-4188-9177-8b7ef0ad9eca@ti.com>
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On Tue, Feb 27, 2024 at 09:54:30AM +0530, Vignesh Raghavendra wrote:
> On 26/02/24 20:05, Th=E9o Lebrun wrote:
> > On Mon Feb 26, 2024 at 12:56 PM CET, Conor Dooley wrote:
> >> On Mon, Feb 26, 2024 at 11:33:06AM +0100, Th=E9o Lebrun wrote:
> >>> Hello Conor,
> >>>
> >>> 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.
> >>>>>
> >>>>> 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(-)
> >>>>>
> >>>>> diff --git a/Documentation/devicetree/bindings/usb/ti,j721e-usb.yam=
l 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 thou=
gh,
> >>>> so I would expect this to actually be:
> >>>> oneOf:
> >>>>   - const: ti,j721e-usb
> >>>>   - items:
> >>>>       - const: ti,am64-usb
> >>>>       - const: ti,j721e-usb
> >>>
> >>> I need your help to grasp what that change is supposed to express? Wo=
uld
> >>> you mind turning it into english sentences?
> >>> A=3Dti,j721e-usb and B=3Dti,am64-usb. My understanding of your propos=
al 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 th=
en
> >>> 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 witho=
ut
> >> 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 ha=
ve
> >> been "A+B" is actually documented as "B+A", but that doesn't make sense
> >> when the originally supported device is "A".

This A and B stuff confused me, I should just have used the actual
compatibles. I meant
| What should have been "B+A" is actually documented as "A+B", 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 suppo=
rt
> >> as a new patch today.
> >=20
> > Thank you for the in-depth explanation! It makes much more sense now,
> > especially the handling of historic stuff that ideally wouldn't have
> > been done this way but that won't be changed from now on.
> >=20
>=20
> IIRC, idea behind adding new compatible for AM64 even though register
> map is very much compatible is just being future proof as AM64 and J721e
> belong to different product groups and thus have differences wrt SoC
> level integration etc which may need SoC specific handling later on.

That is fine, I don't think anyone here is disputing a soc-specific
compatible existing for this device.

> Also, note that AM64 SoC support was added long after J721e. So ideally
> should be B+A if at all we need a fallback compatible.

Correct, I accidentally wrote "A+B", but you can see that that
conflicted with the actual example I had given above.

> I don't see any DT (now or in the past) using
>=20
> compatible =3D B,A or compatible =3D A,B
>=20
> So do we really need A+B to be supported by binding?

Given the mistake, I am going to take this as meaning should the
fallback be supported. My take is that if we are going to remove
something, it should be "ti,am64-usb" isolation that should go.
The devicetrees can be update without concerns about compatibility.

Cheers,
Conor.


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