linux-kernel - Re: [PATCH v3 3/5] media: dt-bindings: media: Add binding for the Raspberry Pi HEVC decoder

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Message-ID: <CAPY8ntCWzp9cRKwLg44G20jG17q2KhavZa_8qpodhGUGS2Bc7Q@mail.gmail.com>
Date: Mon, 28 Apr 2025 11:03:57 +0100
From: Dave Stevenson <dave.stevenson@...pberrypi.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, John Cox <john.cox@...pberrypi.com>, 
	Dom Cobley <dom@...pberrypi.com>, review list <kernel-list@...pberrypi.com>, 
	Ezequiel Garcia <ezequiel@...guardiasur.com.ar>, John Cox <jc@...esim.co.uk>, 
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 3/5] media: dt-bindings: media: Add binding for the
 Raspberry Pi HEVC decoder

Hi Krzysztof

On Fri, 25 Apr 2025 at 08:53, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On Wed, Apr 23, 2025 at 06:20:20PM GMT, Dave Stevenson wrote:
> > Adds a binding for the HEVC decoder found on th +maintainers:
> > +  - John Cox <john.cox@...pberrypi.com>
> > +  - Dom Cobley <dom@...pberrypi.com>
> > +  - Dave Stevenson <dave.stevenson@...pberrypi.com>
>
> > +  - Raspberry Pi internal review list <kernel-list@...pberrypi.com>
>
> Drop, no mailing lists in bindings maintainers. These must be people.

Ack

> > +
> > +description:
> > +  The Raspberry Pi HEVC decoder is a hardware video decode accelerator block
> > +  found in the BCM2711 and BCM2712 processors used on Raspberry Pi 4 and 5
> > +  boards respectively.
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - enum:
> > +          - brcm,bcm2711-hevc-dec
> > +          - brcm,bcm2712-hevc-dec
> > +      - const: raspberrypi,hevc-dec
>
> Not what Rob asked. You should use specific SoC compatible as fallback.

In which case I don't understand what Rob was asking for.
I asked for clarification in [1], but got no reply. Sending a new
version has at least got an answer, but I'm none the wiser.

Staring at this trying to work out your meaning, you want the generic
first, and SoC specific second? ie
+  compatible:
+    items:
+      - const: raspberrypi,hevc-dec
+      - enum:
+          - brcm,bcm2711-hevc-dec
+          - brcm,bcm2712-hevc-dec

> You referred to file "raspberrypi,pisbe.yaml" before, but there is no
> such file in the next.

Typo.
https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/media/raspberrypi%2Cpispbe.yaml
Reviewed by Rob only just over a year ago [2]

> Before you reply that there is a binding using different rules: well,
> there is always poor code. Above two comments are repeated, especially
> this about specific compatible - all the time, so these are not new
> rules. These are given in reviews since some years.

My Google-foo is totally failing with the only directly relevant
mention of "fallback compatible" I find is [3], which just says to use
them.

You're effectively saying I can't take anything in the kernel tree as
being a valid example as it could be poor code, and a layman such as
myself has no way of telling.
Could you please point me at documentation and examples I can rely on,
or educate me with what is wanted in this situation to avoid me having
to guess?

A further mailing list search has brought up [4] which is a thread
with yourself from 2 years ago which looks to be a very similar
situation. Other than missing the const on the SoC strings (although
that isn't in the merged version of cnm,wave521c.yaml), and two SoC
specific strings, I'm not seeing an obvious difference between there
and here either.

Many thanks
  Dave

> Best regards,
> Krzysztof

[1] https://lore.kernel.org/linux-media/CAPY8ntD3Frq5HzV06OrS1051QfjJFzvqs9H4mUkVnd4QKqiMhg@mail.gmail.com/
[2] https://www.spinics.net/lists/linux-media/msg250095.html
[3] https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-bindings.html#properties
[4] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20230929-wave5_v13_media_master-v13-6-5ac60ccbf2ce@collabora.com/#25567148