linux-kernel - Re: [PATCH v4 2/9] dt-bindings: display: add verisilicon,dc

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Message-ID: <CAL_JsqKC6FaJZubvxQaX-uQBhWFNs2EHuTG8JK1FJaD1tPOaSw@mail.gmail.com>
Date: Mon, 5 Jan 2026 10:20:40 -0600
From: Rob Herring <robh@...nel.org>
To: Icenowy Zheng <uwu@...nowy.me>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Drew Fustini <fustini@...nel.org>, Guo Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Heiko Stuebner <heiko@...ech.de>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Michal Wilczynski <m.wilczynski@...sung.com>, Han Gao <rabenda.cn@...il.com>, 
	Yao Zi <ziyao@...root.org>, dri-devel@...ts.freedesktop.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 2/9] dt-bindings: display: add verisilicon,dc

On Mon, Jan 5, 2026 at 10:13 AM Icenowy Zheng <uwu@...nowy.me> wrote:
>
> 在 2026-01-05星期一的 09:46 -0600，Rob Herring写道：
> > On Thu, Dec 25, 2025 at 12:11:58AM +0800, Icenowy Zheng wrote:
> > > From: Icenowy Zheng <uwu@...nowy.me>
> > >
> > > Verisilicon has a series of display controllers prefixed with DC
> > > and
> > > with self-identification facility like their GC series GPUs.
> > >
> > > Add a device tree binding for it.
> > >
> > > Depends on the specific DC model, it can have either one or two
> > > display
> > > outputs, and each display output could be set to DPI signal or "DP"
> > > signal (which seems to be some plain parallel bus to HDMI
> > > controllers).
> > >
> > > Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
> > > Signed-off-by: Icenowy Zheng <zhengxingda@...as.ac.cn>
> > > ---
> > > Changes in v4:
> > > - Added a comment for "verisilicon,dc" that says the ID/revision is
> > >   discoverable via registers.
> > > - Removed clock minItems constraint w/o specific compatible
> > > strings.
> > >
> > > Changes in v3:
> > > - Added SoC-specific compatible string, and arm the binding with
> > > clock /
> > >   port checking for the specific SoC (with a 2-output DC).
> > >
> > > Changes in v2:
> > > - Fixed misspelt "versilicon" in title.
> > > - Moved minItems in clock properties to be earlier than items.
> > > - Re-aligned multi-line clocks and resets in example.
> > >
> > >  .../bindings/display/verisilicon,dc.yaml      | 144
> > > ++++++++++++++++++
> > >  1 file changed, 144 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/display/verisilicon,dc.yaml
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/display/verisilicon,dc.yaml
> > > b/Documentation/devicetree/bindings/display/verisilicon,dc.yaml
> > > new file mode 100644
> > > index 0000000000000..fe64cc1466690
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/verisilicon,dc.yaml
> > > @@ -0,0 +1,144 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/display/verisilicon,dc.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Verisilicon DC-series display controllers
> > > +
> > > +maintainers:
> > > +  - Icenowy Zheng <uwu@...nowy.me>
> > > +
> > > +properties:
> > > +  $nodename:
> > > +    pattern: "^display@[0-9a-f]+$"
> > > +
> > > +  compatible:
> > > +    items:
> > > +      - enum:
> > > +          - thead,th1520-dc8200
> > > +      - const: verisilicon,dc # DC IPs have discoverable
> > > ID/revision registers
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  interrupts:
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    items:
> > > +      - description: DC Core clock
> > > +      - description: DMA AXI bus clock
> > > +      - description: Configuration AHB bus clock
> > > +      - description: Pixel clock of output 0
> > > +      - description: Pixel clock of output 1
> > > +
> > > +  clock-names:
> > > +    items:
> > > +      - const: core
> > > +      - const: axi
> > > +      - const: ahb
> > > +      - const: pix0
> > > +      - const: pix1
> > > +
> > > +  resets:
> > > +    items:
> > > +      - description: DC Core reset
> > > +      - description: DMA AXI bus reset
> > > +      - description: Configuration AHB bus reset
> > > +
> > > +  reset-names:
> > > +    items:
> > > +      - const: core
> > > +      - const: axi
> > > +      - const: ahb
> > > +
> > > +  ports:
> > > +    $ref: /schemas/graph.yaml#/properties/ports
> > > +
> > > +    properties:
> > > +      port@0:
> > > +        $ref: /schemas/graph.yaml#/properties/port
> > > +        description: The first output channel , endpoint 0 should
> > > be
> >
> > No space before comma. Or perhaps should be a period instead.
>
> Well I don't know why I inserted such a space, will remove it.
>
> >
> >
> > > +          used for DPI format output and endpoint 1 should be used
> > > +          for DP format output.
> > > +
> > > +      port@1:
> > > +        $ref: /schemas/graph.yaml#/properties/port
> > > +        description: The second output channel if the DC variant
> > > +          supports. Follow the same endpoint addressing rule with
> > > +          the first port.
> > > +
> > > +    required:
> > > +      - port@0
> > > +
> > > +required:
> > > +  - compatible
> > > +  - reg
> > > +  - interrupts
> > > +  - clocks
> > > +  - clock-names
> > > +  - ports
> > > +
> > > +allOf:
> > > +  - if:
> > > +      properties:
> > > +        compatible:
> > > +          contains:
> > > +            const: thead,th1520-dc8200
> > > +    then:
> > > +      properties:
> > > +        clocks:
> > > +          minItems: 5
> >
> > That's already implicitly the min. Perhaps you wanted 'minItems: 4'
> > on
> > the clocks and clock-names definitions for versions with only 1
> > output?
>
> Previously I specified minItems: 4 in the general part, however this
> does not play well when some of core/axi/ahb clocks are not present.

I don't understand. That would only make pix1 optional. There of
course is no way we can check that 'clocks' entries are pointing to
the correct clocks.

> > > +        ports:
> > > +          required:
> > > +            - port@0
> > > +            - port@1
> >
> > It is valid to omit these if the output is present, but unused.
>
> Well this sounds reasonable, although my driver does not play well if
> only a port@1 is defined w/o port@0 .

Sounds like your driver should be fixed.

> Considering the previous two snippets, should I just remove this if
> part?

I would, yes.

Rob