Re: [PATCH v5 2/7] dt-bindings: PCI: ti,am65: Extend for use with PVU

[Krzysztof Kozlowski]

On 09/09/2024 08:48, Jan Kiszka wrote:
> On 09.09.24 08:22, Krzysztof Kozlowski wrote:
>> On Sun, Sep 08, 2024 at 07:32:28PM +0200, Jan Kiszka wrote:
>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>>>
>>> The PVU on the AM65 SoC is capable of restricting DMA from PCIe devices
>>> to specific regions of host memory. Add the optional property
>>> "memory-regions" to point to such regions of memory when PVU is used.
>>>
>>> Since the PVU deals with system physical addresses, utilizing the PVU
>>> with PCIe devices also requires setting up the VMAP registers to map the
>>> Requester ID of the PCIe device to the CBA Virtual ID, which in turn is
>>> mapped to the system physical address. Hence, describe the VMAP
>>> registers which are optional unless the PVU shall be used for PCIe.
>>>
>>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>>> ---
>>> CC: Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
>>> CC: "Krzysztof Wilczyński" <kw@xxxxxxxxx>
>>> CC: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>>> CC: linux-pci@xxxxxxxxxxxxxxx
>>> ---
>>>  .../bindings/pci/ti,am65-pci-host.yaml        | 29 +++++++++++++++++--
>>>  1 file changed, 26 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/pci/ti,am65-pci-host.yaml b/Documentation/devicetree/bindings/pci/ti,am65-pci-host.yaml
>>> index 0a9d10532cc8..0c297d12173c 100644
>>> --- a/Documentation/devicetree/bindings/pci/ti,am65-pci-host.yaml
>>> +++ b/Documentation/devicetree/bindings/pci/ti,am65-pci-host.yaml
>>> @@ -20,14 +20,18 @@ properties:
>>>        - ti,keystone-pcie
>>>  
>>>    reg:
>>> -    maxItems: 4
>>> +    minItems: 4
>>> +    maxItems: 6
>>>  
>>>    reg-names:
>>> +    minItems: 4
>>>      items:
>>>        - const: app
>>>        - const: dbics
>>>        - const: config
>>>        - const: atu
>>> +      - const: vmap_lp
>>> +      - const: vmap_hp
>>>  
>>>    interrupts:
>>>      maxItems: 1
>>> @@ -83,13 +87,30 @@ if:
>>>      compatible:
>>>        enum:
>>>          - ti,am654-pcie-rc
>>> +
>>>  then:
>>> +  properties:
>>> +    memory-region:
>>
>> I think I said it two times already. You must define properties in
>> top-level. That's how we expect, that's how dtschema works (even if it
>> works fine otherwise, it's not always that case), that's how almost all
>> bindings are written.
> 
> Look, if you have such rules, also enhance the checker, or people like
> me will continue to work intuitively. Add reasoning along that as well,

That would be ideal, but I also asked to do this twice. It does not
matter if dtschema  or me tells you this, if you do not implement it.

> would help further to reduce your review effort. The current situation
> with rather fuzzy results from the checker and strange mechanisms inside
> (see my maxItems finding) is not very helpful IMHO.
> 
> I this concrete case, I would add this item top-level, just to set
> maxItems to 0 for ti,keystone-pcie? Not a pattern I'm finding anywhere.
> Or do we have to allow memory-regions for all compatibles now?

Is it really not suitable for all the compatibles? Maybe these are quite
different devices in such case?

But if it is not really suitable, then you can disallow it for other
variants with :false. This is also explicitly documented in example-schema:
https://elixir.bootlin.com/linux/v5.19/source/Documentation/devicetree/bindings/example-schema.yaml#L212

> 
> Sorry for all these iterations, but you should see from my questions and
> actions where the problems in the concepts are.

Best regards,
Krzysztof