Re: [PATCH 2/3] dt-bindings: media: i2c: Add vision-components,mipi-module-controller

[Richard Leitner <richard.leitner@linux.dev>]

On Wed, Sep 16, 2026 at 10:35:22AM +0200, Krzysztof Kozlowski wrote:
> On 16/09/2026 09:33, Richard Leitner wrote:
> > Hi Krzysztof,
> > 
> > thanks for the review!
> > 
> > On Wed, Sep 16, 2026 at 09:00:46AM +0200, Krzysztof Kozlowski wrote:
> >> On Tue, Sep 15, 2026 at 10:20:24PM +0200, Richard Leitner wrote:
> >>> Add bindings for the Vision Components MIPI Camera Module Controller.
> >>>
> >>> Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
> >>> ---
> >>>  .../vision-components,mipi-module-controller.yaml  | 92 ++++++++++++++++++++++
> >>>  MAINTAINERS                                        |  7 ++
> >>>  2 files changed, 99 insertions(+)
> >>
> >> This fails tests, so a very brief review / a few comments:
> > 
> > Mea culpa, I simply failed to run the dtb check before submitting. Sorry.
> > Will not happen again.
> > 
> >>
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/media/i2c/vision-components,mipi-module-controller.yaml b/Documentation/devicetree/bindings/media/i2c/vision-components,mipi-module-controller.yaml
> >>> new file mode 100644
> >>> index 0000000000000..2a031aea68457
> >>> --- /dev/null
> >>> +++ b/Documentation/devicetree/bindings/media/i2c/vision-components,mipi-module-controller.yaml
> >>> @@ -0,0 +1,92 @@
> >>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> >>> +%YAML 1.2
> >>> +---
> >>> +$id: http://devicetree.org/schemas/media/i2c/vision-components,mipi-module-controller.yaml#
> >>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >>> +
> >>> +title: Vision Components MIPI Camera Module Controller
> >>> +
> >>> +maintainers:
> >>> +  - Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >>> +  - Richard Leitner <richard.leitner@linux.dev>
> >>> +
> >>> +description: |-
> >>> +  The MIPI camera module controller is an FPGA-based, I2C-accessible system
> >>> +  controller found on MIPI camera modules from Vision Components. It abstracts
> >>> +  the camera sensor behind a unified register interface, and controls and
> >>> +  sequences the on-board power supplies and clocks.
> >>> +
> >>> +  The camera sensor abstraction is optional. The controller exposes a tunneled
> >>> +  downstream I2C bus used by the attached image sensor. The controller node
> >>> +  acts as the upstream device on the host bus, while child node below the
> >>> +  controller represent the sensor device reachable through the tunnel.
> >>> +
> >>> +properties:
> >>> +  compatible:
> >>> +    const: vision-components,mipi-module-controller
> >>
> >> There is no model name, no version, nothing identifying it better?
> >> Compatible must be specific to the device (see also writing bindings).
> > 
> > There is one FPGA implemenation for all Vision Components MIPI camera
> > modules AFAICT. So I have no idea how it could be more specific, TBH...
> > 
> > Adding the FPGA hardware model/type is wrong IMHO as it depends on its
> > configuration/firmware, not the hw.
> > 
> > There are different versions of the configuration/firmware. But I think
> > this is also not the correct way to distinguish those, or is it?
> > 
> > According to their homepage the vendor calls those modules simply
> > "VC MIPI" modules, which implies this FPGA controller is available on it.
> > So maybe "vision-components,vc-mipi-controller" would be a better fit?
> > 
> > Do you have any ideas/feedback on how improve this name?
> 
> So there are different modules? I see several different names on:
> https://www.mipi-modules.com/en/mipi-camera-modules/

Yes, there are different modules, but all feature the same controller.
Which this is basically the device driver binding for. So the idea is to
describe the controller independently from the sensor which is "behind"
it.

This works because the controller "soft-core" should be the same on all
modules. A downstream implemenation (which I haven't studied in detail)
is available at https://github.com/VC-MIPI-modules/vc_mipi_core if that
helps?

> 
> 
> > 
> >>
> >>> +
> >>> +  reg:
> >>> +    maxItems: 1
> >>> +
> >>> +  '#clock-cells':
> >>> +    const: 0
> >>> +
> >>> +  clock-frequency:
> >>> +    description: Frequency of the sensor clock provided by the module
> >>
> >> Drop, implied by the compatible
> >>
> > 
> > Do you mean dropping the whole property, or just the "description"?
> 
> I meant entire property, but we keep discussing in Laurent's reply.
> 
> > 
> >>> +
> >>> +  vcc-supply:
> >>> +    description: Power supply of the module (3.3V)
> >>> +
> >>> +  '#address-cells':
> >>> +    const: 1
> >>> +
> >>> +  '#size-cells':
> >>> +    const: 0
> >>
> >> No children allowed, so why these two?
> > 
> > Based on your and the bot feedback I would suggest for v2 to change this
> > "generic i2c bus" to a simple "i2c-tunnel" property which has
> > "$ref: /schemas/i2c/i2c-controller.yaml".
> > 
> > This would better reflect the actual hardware, as there is only this one,
> > in firmware hard-coded I2C downstream bus.
> > 
> > Would this be a sane approach?
> 
> If the underlying I2C bus and sensor are important, then yes. But I have
> doubts that you need to describe the sensor if it is truly
> unadressable/invisible to the OS.

Yes, the I2C bus and sensor is important. The device driver of the sensor
talks (via the tunneled I2C interface) directly to the sensor.

The separate I2C controller/bus description is necessary as the tunneled
I2C bus has some quirks unfortunately. Those need to be addressed as 
otherwise the sensor drivers do not work.

So the idea is to not have a vc-mipi module binding per "sensor variant"
of the camera modules, but provide a common controller driver which
provides the I2C bus for the sensor driver.

> 
> > 
> >>
> >>> +
> >>> +required:
> >>> +  - compatible
> >>> +  - reg
> >>> +  - '#clock-cells'
> >>> +  - clock-frequency
> >>> +  - vcc-supply
> >>> +  - '#address-cells'
> >>> +  - '#size-cells'
> >>> +
> >>> +unevaluatedProperties: false
> >>
> >> additionalProperties instead, see writing bindings or writing schema.
> >> Unless you miss here some other schema $ref.
> >>
> >>> +
> >>> +examples:
> >>> +  - |
> >>> +    i2c {
> >>> +        #address-cells = <1>;
> >>> +        #size-cells = <0>;
> >>> +
> >>> +        vc_mipi_ctrl: controller@10 {
> >>> +            compatible = "vision-components,mipi-module-controller";
> >>> +            reg = <0x10>;
> >>> +            #clock-cells = <0>;
> >>> +            clock-frequency = <37125000>;
> >>> +            vcc-supply = <&cam_3v3>;
> >>> +
> >>> +            #address-cells = <1>;
> >>> +            #size-cells = <0>;
> >>> +
> >>> +            i2c@0 {
> >>> +                #address-cells = <1>;
> >>> +                #size-cells = <0>;
> >>> +
> >>> +                vc_mipi_sensor: camera@60 {
> >>> +                    compatible = "ovti,ov9281";
> >>> +                    reg = <0x60>;
> >>
> >> Why having the child abstraction if it is completely abstracted? I don't
> >> fully get the explanation from description. Completely optional means no
> >> benefits, no point in it, no?
> > 
> > I will try to improve the description. The idea behind this device
> > driver/devicetree node is to not rely on the sensor abstraction from
> > vision components, but to use the upstream sensor specific driver.
> 
> You can use driver even without these nodes... but fine, let's assume
> you have them, so driver will talk with OV9281 sensor for example?

The vc-mipi driver does not talk to sensor at all. This is done by the
dedicated sensor driver. The vc-mipi driver is only controlling the
regulator, clock, etc. as described and sets up the "quirk aware"
tunneled i2c interface.

> 
> > 
> > As the tunneled downstream i2c bus needs quirks applied this is modeled
> > as a separate bus.
> > 
> > Previous discussions on this approach are available at:
> > 	https://lore.kernel.org/lkml/20260728092856.GB1494774@killaraus.ideasonboard.com/
> > 
> Best regards,
> Krzysztof

If you have any other questions or something is still unclear to you,
please feel free to reach out!

regards;rl