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

[Krzysztof Kozlowski <krzk@kernel.org>]

On 16/09/2026 16:57, Richard Leitner wrote:
>>>>>>> +  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.
> 
> From that point of view, of course all variants are different.
> But the interface towards the host is (according to vision components)
> stable. This is why I aimed for a separate device.

What makes you think that interface is stable and the same? Is the
stable aspect or its versioning documented anywhere in the docs?

I can easily imagine that FPGA synthesis actually differs on some
sensors or they ship a new, updated version, thus at some point the
interface might change or already changed between models.

> 
> So what's your suggestion on how to best solve this?
> Provide a per sensor compatible like e.g. "vc-mipi-ov9281"?
> 
> Nonehteless this device must then provide a i2c sub node to place the
> actual imaging sensor on.
> 
> If that's fine with you I'm personally fine with this approach too.
If you have certainty, like documented spec somewhere telling this, that
programming interface of FPGA to the OS is the same, then go with a
generic fallback compatible like you have and add front compatibles
specific to the sensor.

If you do not have certainty, then I would go only with sensor-specific
compatibles for both front and fallbacks, so:

vc-mipi-ov9281, vc-mipi-imx297

It does feel a bit odd, but that is usual way to handle any future
differences when two vc-mipi modules turn out not to be compatible.

Best regards,
Krzysztof