Re: [Patch v15 4/5] dt-bindings: arm-smmu: Add bindings for qcom,smmu-v2

From: Rob Herring
Date: Wed Aug 29 2018 - 20:43:46 EST


On Wed, Aug 29, 2018 at 6:23 AM Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
>
> On Wed, Aug 29, 2018 at 2:05 PM Vivek Gautam
> <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> >
> > Hi Rob,
> >
> >
> > On 8/29/2018 2:04 AM, Rob Herring wrote:
> > > On Mon, Aug 27, 2018 at 04:25:50PM +0530, Vivek Gautam wrote:
> > >> Add bindings doc for Qcom's smmu-v2 implementation.
> > >>
> > >> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> > >> Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > >> Tested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > >> ---
> > >>
> > >> Changes since v14:
> > >> - This is a new patch added in v15 after noticing the new
> > >> checkpatch warning for separate dt-bindings doc.
> > >> - This patch also addresses comments given by Rob and Robin to add
> > >> a list of valid values of '<soc>' in "qcom,<soc>-smmu-v2"
> > >> compatible string.
> > >>
> > >> .../devicetree/bindings/iommu/arm,smmu.txt | 47 ++++++++++++++++++++++
> > >> 1 file changed, 47 insertions(+)
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > >> index 8a6ffce12af5..52198a539606 100644
> > >> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > >> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> > >> @@ -17,10 +17,24 @@ conditions.
> > >> "arm,mmu-401"
> > >> "arm,mmu-500"
> > >> "cavium,smmu-v2"
> > >> + "qcom,<soc>-smmu-v2", "qcom,smmu-v2"
> > > The v2 in the compatible string is kind of redundant unless the SoC has
> > > other SMMU types.
> >
> > sdm845 has smmu-v2, and smmu-500 [1].
> >
> > >>
> > >> depending on the particular implementation and/or the
> > >> version of the architecture implemented.
> > >>
> > >> + A number of Qcom SoCs use qcom,smmu-v2 version of the IP.
> > >> + "qcom,<soc>-smmu-v2" represents a soc specific compatible
> > >> + string that should be present along with the "qcom,smmu-v2"
> > >> + to facilitate SoC specific clocks/power connections and to
> > >> + address specific bug fixes.
> > >> + '<soc>' string in "qcom,<soc>-smmu-v2" should be one of the
> > >> + following:
> > >> + msm8996 - for msm8996 Qcom SoC.
> > >> + sdm845 - for sdm845 Qcom Soc.
> > > Rather than all this prose, it would be simpler to just add 2 lines with
> > > the full compatibles rather than <soc>. The <soc> thing is not going to
> > > work when/if we move bindings to json-schema also.
> >
> > then we keep adding
> > "qcom,msm8996-smmu-v2", "qcom,smmu-v2"
> > "qcom,msm8998-smmu-v2", "qcom,smmu-v2"
> > "qcom,sdm845-smmu-v2", "qcom,smmu-v2",
> > and from [1]
> > "qcom,sdm845-smmu-500", "arm,mmu-500", etc.
> > for each SoCs?
>
> How about following diff on top of this patch?
>
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> index 52198a539606..5e6c04876533 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
> @@ -17,23 +17,18 @@ conditions.
> "arm,mmu-401"
> "arm,mmu-500"
> "cavium,smmu-v2"
> - "qcom,<soc>-smmu-v2", "qcom,smmu-v2"
> + "qcom,smmu-v2"
>
> depending on the particular implementation and/or the
> version of the architecture implemented.
>
> - A number of Qcom SoCs use qcom,smmu-v2 version of the IP.
> - "qcom,<soc>-smmu-v2" represents a soc specific compatible
> - string that should be present along with the "qcom,smmu-v2"
> - to facilitate SoC specific clocks/power connections and to
> - address specific bug fixes.
> - '<soc>' string in "qcom,<soc>-smmu-v2" should be one of the
> - following:
> - msm8996 - for msm8996 Qcom SoC.
> - sdm845 - for sdm845 Qcom Soc.
> -
> - An example string would be -
> - "qcom,msm8996-smmu-v2", "qcom,smmu-v2".
> + Qcom SoCs using qcom,smmu-v2 must have soc specific
> + compatible string attached to "qcom,smmu-v2" to take care
> + of SoC specific clocks/power connections and to address
> + specific bug fixes.
> + Precisely, it should be one of the following:
> + "qcom,msm8996-smmu-v2", "qcom,smmu-v2",
> + "qcom,sdm845-smmu-v2", "qcom,smmu-v2".

We don't need an explanation of why we need specific compatibles in
each binding document (though maybe we need a better explanation
somewhere). We just need to know what are valid values for compatibles
and this includes any combinations. Generally, this is just a list of
combinations.

The Renesas folks have figured out how to do this and they have lots
of SoCs. Yes, it makes for a lot of patches, but they are all mostly 1
liners and are dead simple to review. With QCom, I'm tired of having
the same damn discussion with every new binding.

Rob