linux-kernel - Re: [PATCH v6 13/52] dt-bindings: memory: tegra124: emc: Document new interconnect property

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Date:   Tue, 27 Oct 2020 20:48:33 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Mikko Perttunen <cyndis@...si.fi>,
        Viresh Kumar <vireshk@...nel.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v6 13/52] dt-bindings: memory: tegra124: emc: Document
 new interconnect property

On Tue, Oct 27, 2020 at 10:19:28PM +0300, Dmitry Osipenko wrote:
> 27.10.2020 13:25, Krzysztof Kozlowski пишет:
> > On Mon, Oct 26, 2020 at 01:16:56AM +0300, Dmitry Osipenko wrote:
> >> External memory controller is interconnected with memory controller and
> >> with external memory. Document new interconnect property which turns
> >> External Memory Controller into interconnect provider.
> >>
> >> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> >> ---
> >>  .../bindings/memory-controllers/nvidia,tegra124-emc.yaml   | 7 +++++++
> >>  1 file changed, 7 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra124-emc.yaml b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra124-emc.yaml
> >> index 278549f9e051..ac00832ceac1 100644
> >> --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra124-emc.yaml
> >> +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra124-emc.yaml
> >> @@ -29,6 +29,9 @@ properties:
> >>      items:
> >>        - const: emc
> >>  
> >> +  "#interconnect-cells":
> >> +    const: 0
> >> +
> >>    nvidia,memory-controller:
> >>      $ref: /schemas/types.yaml#/definitions/phandle
> >>      description:
> >> @@ -327,6 +330,7 @@ required:
> >>    - clocks
> >>    - clock-names
> >>    - nvidia,memory-controller
> >> +  - "#interconnect-cells"
> > 
> > Another required property, what about all existing users of this binding?
> 
> EMC/devfreq drivers check presence of the new properties and ask users
> to upgrade the DT. The kernel will continue to work fine using older
> DTBs, but devfreq driver won't load.

If the devfreq was working fine before (with these older DTBs and older
kernel) then you break the feature.

If devfreq was not working or was not stable enough, then nothing is
broken so such change is accepted.

Which one is then?

> 
> >>  additionalProperties: false
> >>  
> >> @@ -345,6 +349,7 @@ examples:
> >>  
> >>          #iommu-cells = <1>;
> >>          #reset-cells = <1>;
> >> +        #interconnect-cells = <1>;
> > 
> > You meant '0'?
> 
> '1' is for the "mc" node in the example (not "emc" node).
> 
> Anyways, I'll move this hunk to the previous patch in order to fix the
> kernel bot warning.

Right, thanks.

Best regards,
Krzysztof