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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 16/09/2026 11:01, Richard Leitner wrote:
> 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.

Bindings must accurately describe the device and so far - based on the
website - there is no device as mipi-module-controller alone.

I don't get why you assume that all of the variants are exactly
identical, thus sensor variant is not applicable.

If they are identical in all aspects, then why clock-frequency property?
That's obviously rhetorical question, because they are not identical in
all aspects and must produce different clock at least.


> 
>>
>>>
>>>>
>>>>> +
>>>>> +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.

I meant, driver for the sensor. So who controls sensor supplies? Not the
sensor driver? It tells something how the hardware is managed, no?
> 
Best regards,
Krzysztof