Re: [PATCH v11 3/7] dt-bindings: PCI: qcom: Use sdx55 reg description for ipq9574

[Varadarajan Narayanan <quic_varada@quicinc.com>]

On Thu, Mar 06, 2025 at 01:06:13PM +0100, Krzysztof Kozlowski wrote:
> On 06/03/2025 12:52, Krzysztof Kozlowski wrote:
> > On 20/02/2025 10:42, Varadarajan Narayanan wrote:
> >> All DT entries except "reg" is similar between ipq5332 and ipq9574. ipq9574
> >> has 5 registers while ipq5332 has 6. MHI is the additional (i.e. sixth
> >> entry). Since this matches with the sdx55's "reg" definition which allows
> >> for 5 or 6 registers, combine ipq9574 with sdx55.
> >>
> >> This change is to prepare ipq9574 to be used as ipq5332's fallback
> >> compatible.
> >>
> >> Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> >> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> >
> > Unreviewed.
> >
> >> Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.com>
> >> ---
> >> v8: Add 'Reviewed-by: Krzysztof Kozlowski'
> >> ---
> >>  Documentation/devicetree/bindings/pci/qcom,pcie.yaml | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
> >> index 7235d6554cfb..4b4927178abc 100644
> >> --- a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
> >> +++ b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
> >> @@ -169,7 +169,6 @@ allOf:
> >>              enum:
> >>                - qcom,pcie-ipq6018
> >>                - qcom,pcie-ipq8074-gen3
> >> -              - qcom,pcie-ipq9574
> >
> > Why you did not explain that you are going to affect users of DTS?
> >
> > NAK

Sorry for not explicitly calling this out. I thought that would be seen from the
following DTS related patches.

> I did not connect the dots, but I pointed out that you break users and
> your DTS is wrong:
> https://lore.kernel.org/all/f7551daa-cce5-47b3-873f-21b9c5026ed2@kernel.org/
>
> so you should come back with questions to clarify what to do, not keep
> pushing this incorrect patchset.
>
> My bad, I should really have zero trust.

It looks like it is not possible to have ipq9574 as fallback (for ipq5332)
without making changes to ipq9574 since the "reg" constraint is different
between the two. And this in turn would break the ABI w.r.t. ipq9574.

To overcome this, two approaches seem to be availabe

	1. Document that ipq9574 is impacted and rework these patches to
	   minimize the impact as much as possible

		(or)

	2. Handle ipq5332 as a separate compatible (without fallback) and reuse
	   the constraints of sdx55 for "reg" and ipq9574 for the others (like
	   clock etc.). This approach will also have to revert [1], as it
	   assumes ipq9574 as fallback.

Please advice which of the above would be appropriate. If there is a better 3rd
alternative please let me know, will align with that approach.

Thanks
Varada

1 - https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/Documentation/devicetree/bindings/pci/qcom,pcie.yaml?id=f67d04b18337249b0faa5cab6223c0bb203f6333