On 24/07/2022 00:50, Dmitry Baryshkov wrote:
> On Sat, 23 Jul 2022 at 20:48, Krzysztof Kozlowski
> <krzysztof.kozlowski@xxxxxxxxxx> wrote:
>>
>> On 23/07/2022 11:09, Dmitry Baryshkov wrote:
>>> Describing each compatible board in DT schema seems wrong to me. It
>>> means that each new board is incompatible by default, until added to the DT
>>> schema.
>
> s/incompatible/non-valid/
>
>>
>> The bindings do not document something because it is or it is no
>> compatible. They document the compatible. Your patch essentially removes
>> the documentation, so there is no point in having compatibles in board
>> at all...
>
> I do not quite agree here. Please correct me if I'm wrong.
> Schema defines which DT files are correct and which are not. Which
> properties are required, which values are valid, etc. So far so good.
Schema is a tool, we create here bindings. The bindings document what
you wrote above, plus compatibles and any other pieces mentioned in DT spec.
> For the device nodes it declares (or is willing to declare) all
> possible compatibility strings. There is a sensible number of on-chip
> IP blocks, external chips, etc. Each and every new chip (or new IP
> block) we are going to have a yaml file describing its usage. Perfect.
> For the machine compatibility lists the arm,qcom schema declares which
> machine compat strings are valid. And this looks like a problem. Now
> for the DT to be fully valid against DT schema, we have to define its
> machine compat string.
Although one of goals is to have schema compliance, that is not the
reason why we document compatibles. Compatibles were documented long
time ago before DT schema came, because the bindings require it.
Bindings define the interface between the DTS and software which uses
it. SW is kernel, bootloaders, user-space and some more.
> For each and every phone/sbc/evb we have to name it in schema. I think
> this is an overkill.
Qualcomm is rather moderate, nothing big here so definitely it is not an
overkill. We almost do not have there SoMs. Just take a pick at
Freescale - this is much more complex than Qualcomm, so any changes
should start with that. Qualcomm's "complexity" is not a reason to do
anything...
> It feels like we are putting DT information
> (mapping form machine compat to SoC) into the DT schema.
No, we are documenting the compatible in bindings. Just like we always
did and we always had to.
> For qcs404 we already have a schema which uses three items: {},
> qcom,qcs404-evb, qcom,qcs404. This sounds like a perfect idea to me.
> We allow any board, created by Qualcomm, Google or any other random
> vendor, named Foo, Bar or Baz, as long as it declares that it is
> compatible with qcom,qcs404-evb.
>
> To go even further. We now have the qrb5165-rb5.dts, declaring
> compatible = "qcom,qrb5165-rb5", "qcom,sm8250".
> If at some point I add a navigation/communication/whatever mezz on top
> of it. It would make sense to use compatible =
> "qcom,qrb5165-rb5-navi-comm", "qcom,qrb5165-rb5", "qcom,sm8250".
> Adding this to the growing list inside arm,qcom.yaml sounds like a
> nightmare. I can only hope that at some point JSON schema gains
> postfixItems support (as proposed) to be able to change e.g.
> arm,qcom.yaml to list just our qcom,something platforms as possible
> postfixItems for the schema.
Again, Qualcomm complexity is nothing compared to Freescale. :)
>
> Regarding having compatibles in board files at all. I think that they
> are somehow misused nowadays. Instead of declaring that the
> Dragonboard 845c is compatible with "thundercomm,db845c",
> "qcom,sdm845-sbc", "96boards,ce-board", "96boards,iot-board",
> "qcom,sdm845", the DT file declares nearly useless
> "thundercomm,db845c", "qcom,sdm845".
>
> Thus, if we (mostly) use machine compatible array to just define
> Vendor+device name and the underlying Qualcomm SoC, I propose to leave
> just a sensible part (SoC) in DT schema, while allowing any string in
> the first part.
No, because you miss then the purpose of bindings - to document the
compatible which is the important piece of interface between
DTS/bootloader/kernel/other OS/user-space.
To summarize, you propose to not document board compatibles. This is not
what we want, because then the next step is - let's don't document SoCs.
If you do not document it, means anyone can uniliteraly change it, e.g.
in kernel DTS, which will break all other users (e.g. user-space or
bootloaders) parsing the compatibles. And before you say - no one parses
the board compatibles - let me just say that several user-space
(embedded/closed) parse them, bootloaders parse them (U-Boot, Google's
Chromebooks and others)
Best regards,
Krzysztof
