linux-kernel - Re: [PATCH 2/2] media: dt-bindings: Use additionalProperties: false for endpoint: properties:

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Message-ID: <20241016092726.GE2712@pendragon.ideasonboard.com>
Date: Wed, 16 Oct 2024 12:27:26 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Dave Stevenson <dave.stevenson@...pberrypi.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Martin Kepplinger <martink@...teo.de>,
	Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
	"Paul J. Murphy" <paul.j.murphy@...el.com>,
	Daniele Alessandrelli <daniele.alessandrelli@...el.com>,
	Tommaso Merciai <tomm.merciai@...il.com>,
	Martin Hecht <martin.hecht@...et.eu>,
	Zhi Mao <zhi.mao@...iatek.com>,
	Alain Volmat <alain.volmat@...s.st.com>,
	Mikhail Rudenko <mike.rudenko@...il.com>,
	Ricardo Ribalda <ribalda@...nel.org>,
	Kieran Bingham <kieran.bingham@...asonboard.com>,
	Umang Jain <umang.jain@...asonboard.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
	Dongchun Zhu <dongchun.zhu@...iatek.com>,
	Quentin Schulz <quentin.schulz@...obroma-systems.com>,
	Todor Tomov <todor.too@...il.com>, linux-media@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] media: dt-bindings: Use additionalProperties: false
 for endpoint: properties:

Hi Krzysztof,

On Tue, Oct 15, 2024 at 01:51:43PM +0200, Krzysztof Kozlowski wrote:
> On 15/10/2024 13:28, Laurent Pinchart wrote:
> > On Tue, Oct 15, 2024 at 08:11:18AM +0200, Krzysztof Kozlowski wrote:
> >> On 14/10/2024 22:29, Laurent Pinchart wrote:
> >>> On Mon, Oct 14, 2024 at 10:47:31AM +0200, Krzysztof Kozlowski wrote:
> >>>> On 14/10/2024 10:31, Bryan O'Donoghue wrote:
> >>>>> On 14/10/2024 08:45, Krzysztof Kozlowski wrote:
> >>>>>> I do not understand the reasoning behind this change at all. I don't
> >>>>>> think DT maintainers ever suggested it (in fact, rather opposite:
> >>>>>> suggested using unevaluatedProps) and I think is not a consensus of any
> >>>>>> talks.
> >>>>>
> >>>>> No there is not but then, how do you give consistent feedback except 
> >>>>> proposing something to be a baseline.
> >>>>>
> >>>>> On the one hand you have upstream additionalProperties: false and 
> >>>>> unevaluatedProperites: false - it'd be better to have a consistent 
> >>>>> message on which is to be used.
> >>>>
> >>>> Well, I am afraid that push towards additionalProps will lead to grow
> >>>> common schema (video-interface-devices or video-interfaces) into huge
> >>>> one-fit-all binding. And that's not good.
> >>>>
> >>>> If a common binding for a group of devices encourages you to list its
> >>>> subset, then it is not that common.
> >>>>
> >>>> Solution is to fix that, e.g. split it per classes of devices.
> >>>
> >>> I think splitting large schemas per class is a good idea, but the
> >>> problem will still exist. For instance, if we were to move the
> >>> CSI-2-specific properties to a separate schema, that schema would define
> >>> clock-lanes, data-lanes and clock-noncontinuous. The clock-lanes and
> >>> clock-noncontinuous properties do not apply to every device, how would
> >>> we then handle that ? I see three options:
> >>
> >> Why is this a problem? Why is this a problem here, but not in other
> >> subsystems having exactly the same case?
> > 
> > I won't talk for other subsystems, but I can say I see value in
> > explicitly expressing what properties are valid for a device in DT
> > bindings both to inform DT authors and to perform validation on DT
> > sources. That's the whole point of YAML schemas, and I can't see a good
> > reason not to use the tooling we have developed when it has an easy way
> > to do the job.
> 
> I understand. The benefit, which you see, comes with complexity of the
> binding and need of listing properties.

I agree, the benefit comes at a cost of additional complexity in the
bindings. For me the benefit outweights the cost here as I find the cost
to be relatively small, but I understand that this is a personal
opinion.

> We do not enforce such rules (narrowing common schema in very strict
> way) in other subsystems, maybe with exception of input and touchscreen
> devices, but there common schema is quite big. And DT maintainers
> suggested to drop such code even for these, BTW.

-- 
Regards,

Laurent Pinchart