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

[Richard Acayan <mailingradian@gmail.com>]

> 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:

    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";

    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.

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).

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?