On 14/07/2022 13:29, Laurent Pinchart wrote: > On Thu, Jul 14, 2022 at 01:23:41PM +0200, Krzysztof Kozlowski wrote: >> On 14/07/2022 13:12, Laurent Pinchart wrote: >>>>>>> One option would be to support the following three compatible values: >>>>>>> >>>>>>> compatible = "melexis,mlx75026", "melexis,mlx7502x"; >>>>>>> compatible = "melexis,mlx75027", "melexis,mlx7502x"; >>>>>>> compatible = "melexis,mlx7502x"; >>>>>>> >>>>>>> The last one only would trigger autodetection. I'm still not sure how to >>>>>>> document that properly in bindings though. >>>>>> >>>>>> I missed that part of binding. >>>>>> >>>>>> Wildcards are not allowed in compatible, so mlx7502x has to go. >>>>> >>>>> Really ? We've had fallback generic compatible strings since the >>>>> beginning. >>>> >>>> Fallback generic compatibles are allowed. Wildcards not. Wildcards were >>>> actually never explicitly allowed, they just slipped in to many >>>> bindings... We have several discussions on this on mailing list, so no >>>> real point to repeat the arguments. >>>> >>>> There is a difference between generic fallback. If the device follows >>>> clear specification and version, e.g. "foo-bar-v4", you can use it for >>>> generic compatible. This is more common in SoC components. Requirement - >>>> there is a clear mapping between versions and SoCs. >>> >>> I'm not sure to see a clear difference between the two concepts. >> >> The clear difference is that you have a versioned and re-usable hardware >> block plus clear mapping which version goes to which SoC. Version >> numbers usually start with 1, not with 75025. 75025 is a model name. > > How about Documentation/devicetree/bindings/serial/renesas,scif.yaml for > instance, where the version number isn't known and the SoC name is used > instead ? Is that acceptable ? This is the second case I mentioned - family of devices where the family fallback is not allowed to be alone. You cannot use just "renesas,scif" in DTS. > > How should we deal with devices that have different models, where the > model is irrelevant to the kernel driver, but relevant to userspace ? > Imagine, for instance, a light sensor with 10 models than only differ by > the filter they use to tune the sensitivity to different light spectrums > ? They are all "compatible" from a software point of view, would the > driver need to list all 10 compatible strings ? I don't understand that example, I mean, what's the problem here? If they are all compatible, you can use only one comaptible, e.g. melexis,mlx75026. If you ever need to differentiate it for user-space, you add specific compatible for the model and you have: melexis,mlx75027, melexis,mlx75026 If user-space needs dedicated compatibles - add them, no one here argues to not to use specific compatibles. >>> For cameras, we often deal with complex pipelines with multiple external >>> devices and multiple IP cores, with drivers that need to communicate >>> with each other to initialize the complete camera system. For instance, >>> each camera-related component in the system registers itself in a media >>> graph that can be queried from userspace and exposes information about >>> all devices, including their model. There's no power up of any device >>> when this query is being performed from userspace. It could possibly be >>> changed (and maybe it should, for reasons unrelated to this discussion), >>> but we're looking at pretty much a complete redesign of V4L2 and MC >>> then. >> >> Is then autodetection a real use case since you have to power up the >> sensor each time system boots and this violates privacy? Several I2C >> sensors do not care about this and they always do it on power up, so >> aren't we solving here something unimportant? > > In a laptop or tablet with a camera sensor, you likely don't want > autodetection. In an industrial device, you don't care, and having the > ability to auto-detect the exact sensor model when booting saves cost in > the production chain as a single image can work across different models. We talk about the case here, not generic. Do you want to have autodetection possible here or not? Best regards, Krzysztof
