Re: [PATCH v2 3/6] dt-bindings: PCI: ti,am65: Extend for use with PVU

Krzysztof Kozlowski
2024-08-27T09:29:21Z

On 27/08/2024 11:22, Jan Kiszka wrote:
> On 27.08.24 08:37, Krzysztof Kozlowski wrote:
>> On Mon, Aug 26, 2024 at 11:50:04PM +0200, Jan Kiszka wrote:
>>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> Describe also the VMAP registers which are needed in order to make use
>>> of the PVU with this PCI host. Furthermore, permit to specify a
>>> restricted DMA pool by phandle.
>>
>> That's an ABI break without explanation why it is necessary.
>>
>
> It is needed in order to support the PVU, as written above.

Above say only that you want a new feature and that's not really
suitable explanation for ABI break, because answer to this is: add new
feature without breaking existing users. But maybe there is a bug or
something does not work or never work or there are no users, don't know.

>
> Previous versions of this binding likely didn't consider this use case
> and therefore didn't describe all registers associated with the hardware.
>
> BTW, if you see a way to add the required registers without breaking
> more than needed, I'm all ears. At least the kernel driver will continue
> to work with older DTs when you disable PVU support or do not add a DMA
> pool to the DT.

If there is no ABI break, because driver still handles correctly old
DTB, then mention it in the commit msg.

Best regards,
Krzysztof