Re: [PATCH v2 1/4] dt-bindings: dma: qcom: gpi: add fallback

[Rob Herring <robh@kernel.org>]

On Fri, Sep 23, 2022 at 06:20:28PM -0400, Richard Acayan wrote:
> > On 23/09/2022 23:09, Richard Acayan wrote:
> > > The drivers are transitioning from matching against lists of specific
> > > compatible strings to matching against smaller lists of more generic
> > > compatible strings. Add a fallback compatible string in the schema to
> > > support this change.
> > 
> > Thanks for the patch. I wished we discussed it a bit more. :)
> 
> Ah, sorry for not replying to your original suggestion. I didn't see the
> opportunity for discussion as this new series wasn't that hard to come up
> with.
> 
> > qcom,gpi-dma does not look like specific enough to be correct fallback,
> > at least not for all of the devices. I propose either a IP block version
> > (which is tricky without access to documentation) or just one of the SoC
> > IP blocks.
> 
> Solution 1:
> 
> Yes, I could use something like qcom,sdm845-gpi-dma. It would be weird to
> see the compatible strings for that, though:

Why is it weird? That's how 'compatible' works. You are saying a new 
implementation is compatible with an older implementation.


>     compatible = "qcom,sdm670-gpi-dma", "qcom,sdm845-gpi-dma";
> 

>     // This would need to be valid in dt schema, suggesting solution 2
>     compatible = "qcom,sdm845-gpi-dma";
>     // This just doesn't make sense
>     compatible = "qcom,sdm845-gpi-dma", "qcom,sdm845-gpi-dma";

Is your question how to get the first one to work, but not the second 
one? You need 'oneOf' with at least an entry for each case with 
different number of compatible strings (1 and 2 entries). There are 
lot's of examples in the tree.

> 
>     compatible = "qcom,sm8150-gpi-dma", "qcom,sdm845-gpi-dma";
> 
>     compatible = "qcom,sm8250-gpi-dma", "qcom,sdm845-gpi-dma";
> 
> Solution 2:
> 
> I could stray from the "soc-specific compat", "fallback compat" and just
> have "qcom,sdm845-gpi-dma" for every SoC.

No.

> Solution 3:
> 
> I found the original mailing list archive for this driver:
> 
> https://lore.kernel.org/linux-arm-msm/20200824084712.2526079-1-vkoul@kernel.org/
> https://lore.kernel.org/linux-arm-msm/20200918062955.2095156-1-vkoul@kernel.org/
> 
> It seems like the author originally handled the ee_offset as a dt property
> and removed it. It was removed because it was a Qualcomm-specific property.
> One option would be to bring this back against the author's wishes (or ask
> the author about it, since they are a recipient).

No.

> 
> Solution 4:
> 
> You mentioned there being an xPU3 block here:
> 
> https://lore.kernel.org/linux-arm-msm/e3bfa28a-ecbc-7a57-a996-042650043514@linaro.org/
> 
> Maybe it's fine to have qcom,gpi-dma-v3?

I don't like made up version numbers. QCom does or did have very 
specific version numbers, but in the end they it tended to be 1 or maybe 
2 SoCs per version. So not really beneficial.

Rob