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

[Krzysztof Kozlowski]

On Tue, Oct 27, 2020 at 11:16:29PM +0300, Dmitry Osipenko wrote:
> 27.10.2020 22:48, Krzysztof Kozlowski пишет:
> > 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@xxxxxxxxx>
> >>>> ---
> >>>>  .../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?
> 
> Definitely the latter. The current devfreq works okay'ish, but we rely
> on hardware to recover from temporal FIFO underflows and it's a
> user-visible problem which this series addresses.

I understand. Fine with me, thanks for explanation.

Best regards,
Krzysztof