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Date:   Wed, 28 Jul 2021 09:33:40 -0600
From:   Rob Herring <robh@...nel.org>
To:     Alex Elder <elder@...e.org>
Cc:     Alex Elder <elder@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Gross, Andy" <agross@...nel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Evan Green <evgreen@...omium.org>, cpratapa@...eaurora.org,
        subashab@...eaurora.org, Alex Elder <elder@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] dt-bindings: net: qcom,ipa: make imem
 interconnect optional

On Mon, Jul 26, 2021 at 9:59 AM Alex Elder <elder@...e.org> wrote:
>
> On 7/23/21 3:52 PM, Rob Herring wrote:
> > On Mon, Jul 19, 2021 at 04:24:54PM -0500, Alex Elder wrote:
> >> On some newer SoCs, the interconnect between IPA and SoC internal
> >> memory (imem) is not used.  Reflect this in the binding by moving
> >> the definition of the "imem" interconnect to the end and defining
> >> minItems to be 2 for both the interconnects and interconnect-names
> >> properties.
> >>
> >> Signed-off-by: Alex Elder <elder@...aro.org>
> >> ---
> >>   .../devicetree/bindings/net/qcom,ipa.yaml      | 18 ++++++++++--------
> >>   1 file changed, 10 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/net/qcom,ipa.yaml b/Documentation/devicetree/bindings/net/qcom,ipa.yaml
> >> index ed88ba4b94df5..4853ab7017bd9 100644
> >> --- a/Documentation/devicetree/bindings/net/qcom,ipa.yaml
> >> +++ b/Documentation/devicetree/bindings/net/qcom,ipa.yaml
> >> @@ -87,16 +87,18 @@ properties:
> >>         - const: ipa-setup-ready
> >>
> >>     interconnects:
> >> +    minItems: 2
> >>       items:
> >> -      - description: Interconnect path between IPA and main memory
> >> -      - description: Interconnect path between IPA and internal memory
> >> -      - description: Interconnect path between IPA and the AP subsystem
> >> +      - description: Path leading to system memory
> >> +      - description: Path between the AP and IPA config space
> >> +      - description: Path leading to internal memory
> >>
> >>     interconnect-names:
> >> +    minItems: 2
> >>       items:
> >>         - const: memory
> >> -      - const: imem
> >>         - const: config
> >> +      - const: imem
> >
> > What about existing users? This will generate warnings. Doing this for
> > the 2nd item would avoid the need for .dts updates:
> >
> > - enum: [ imem, config ]
>
> If I understand correctly, the effect of this would be that
> the second item can either be "imem" or "config", and the third
> (if present) could only be "imem"?

Yes for the 2nd, but the 3rd item could only be 'config'.

>
> And you're saying that otherwise, existing users (the only
> one it applies to at the moment is "sdm845.dtsi") would
> produce warnings, because the interconnects are listed
> in an order different from what the binding specifies.
>
> Is that correct?

Yes.

> If so, what you propose suggests "imem" could be listed twice.
> It doesn't make sense, and maybe it's precluded in other ways
> so that's OK.

Good observation. There are generic checks that the strings are unique.

>  But I'd be happy to update "sdm845.dtsi" to
> address your concern.  (Maybe that's something you would rather
> avoid?)

Better to not change DT if you don't have to. You're probably okay if
all clients (consumers of the dtb) used names and didn't care about
the order. And I have no idea if all users of SDM845 are okay with a
DTB change being required. That's up to QCom maintainers. I only care
that ABI breakages are documented as such.

> Also, I need to make a separate update to "sm8350.dtsi" because
> that was defined before I understood what I do now about the
> interconnects.  It uses the wrong names, and should combine
> its first two interconnects into just one.

If the interconnects was ignored in that case, then the change doesn't matter.

Rob

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