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Date:   Wed, 29 Aug 2018 19:43:30 -0500
From:   Rob Herring <robh@...nel.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        alex.williamson@...hat.com,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Stephen Boyd <sboyd@...nel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <andy.gross@...aro.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [Patch v15 4/5] dt-bindings: arm-smmu: Add bindings for qcom,smmu-v2

On Wed, Aug 29, 2018 at 6:23 AM Vivek Gautam
<vivek.gautam@...eaurora.org> wrote:
>
> On Wed, Aug 29, 2018 at 2:05 PM Vivek Gautam
> <vivek.gautam@...eaurora.org> 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@...eaurora.org>
> > >> Reviewed-by: Tomasz Figa <tfiga@...omium.org>
> > >> Tested-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> > >> ---
> > >>
> > >> 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

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