Re: [PATCH v4 14/14] Documentation: KHO: Add memblock bindings

[Krzysztof Kozlowski <krzk@kernel.org>]

On 09/02/2025 21:41, Mike Rapoport wrote:
> On Sun, Feb 09, 2025 at 04:23:09PM +0100, Krzysztof Kozlowski wrote:
>> On 09/02/2025 16:10, Mike Rapoport wrote:
>>> On Sun, Feb 09, 2025 at 11:29:41AM +0100, Krzysztof Kozlowski wrote:
>>>> On 06/02/2025 14:27, Mike Rapoport wrote:
>>>>> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>>>>>
>>>>> We introduced KHO into Linux: A framework that allows Linux to pass
>>>>> metadata and memory across kexec from Linux to Linux. KHO reuses fdt
>>>>> as file format and shares a lot of the same properties of firmware-to-
>>>>> Linux boot formats: It needs a stable, documented ABI that allows for
>>>>> forward and backward compatibility as well as versioning.
>>>>
>>>> Please use subject prefixes matching the subsystem. You can get them for
>>>> example with `git log --oneline -- DIRECTORY_OR_FILE` on the directory
>>>> your patch is touching. For bindings, the preferred subjects are
>>>> explained here:
>>>> https://www.kernel.org/doc/html/latest/devicetree/bindings/submitting-patches.html#i-for-patch-submitters
>>>  
>>> These are not devicetree binding for communicating data from firmware to
>>> the kernel. These bindings are specific to KHO which is perfectly
>>> reflected by the subject.
>>
>> No, it is not. None of the bindings use above subject prefix.
>>
>>>
>>> Just a brief reminder from v2 discussion:
>>> (https://lore.kernel.org/linux-mm/20231222193607.15474-1-graf@amazon.com/)
>>>
>>> "For quick reference: KHO is a new mechanism this patch set introduces 
>>> which allows Linux to pass arbitrary memory and metadata between kernels 
>>> on kexec. I'm reusing FDTs to implement the hand over protocol, as 
>>> Linux-to-Linux boot communication holds very similar properties to 
>>> firmware-to-Linux boot communication. So this binding is not about 
>>> hardware; it's about preserving Linux subsystem state across kexec.
>>
>> does not matter. You added file to ABI documentation so you must follow
>> that ABI documentation rules. One rule is proper subject prefix.
>  
> No, it does not. It's a different ABI.
> 
> FDT is a _data structure_ that provides cross platform unified, versioned,
> introspectable data format.
> 
> Documentation/devicetree/bindings standardizes it's use for describing
> hardware, but KHO uses FDT _data structure_ to describe state of the kernel
> components that will be reused by the kexec'ed kernel.
> 
> KHO is a different namespace from Open Firmware Device Tree, with different
> requirements and different stakeholders. Putting descriptions of KHO data
> formats in Documentation/kho rather than in
> Documentation/devicetree/bindings was not done to evade review of Open
> Firmware Device Tree maintainers, but rather to emphasize that KHO FDT _is
> not_ Open Firmware Device Tree.


Ah, neat, that would almost solve the problem but you wrote:

+$id: http://devicetree.org/schemas/memblock/reserve_mem.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#

so no, this does not work like that. You use devicetree here namespace
and ignore its rules.

You cannot pretend this is not devicetree if you put it into devicetree
schemas.

Best regards,
Krzysztof