linux-kernel - Re: [PATCH 05/10] dt-bindings: interconnect: Add sm8350, sc8280xp and generic OSM L3 compatibles

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Date:   Thu, 3 Nov 2022 10:46:53 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Georgi Djakov <djakov@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sibi Sankar <quic_sibis@...cinc.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Mike Tipton <quic_mdtipton@...cinc.com>,
        Johan Hovold <johan+linaro@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/10] dt-bindings: interconnect: Add sm8350, sc8280xp
 and generic OSM L3 compatibles

On Thu, Nov 03, 2022 at 08:25:17AM -0400, Krzysztof Kozlowski wrote:
> On 02/11/2022 23:44, Bjorn Andersson wrote:
> > On Fri, Oct 28, 2022 at 06:12:29PM -0400, Krzysztof Kozlowski wrote:
> >> On 27/10/2022 23:41, Bjorn Andersson wrote:
> >>> Add EPSS L3 compatibles for sm8350 and sc8280xp, but while at it also
> >>> introduce generic compatible for both qcom,osm-l3 and qcom,epss-l3.
> >>>
> >>> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> >>> ---
> >>>  .../bindings/interconnect/qcom,osm-l3.yaml    | 22 +++++++++++++------
> >>>  1 file changed, 15 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml b/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
> >>> index bf538c0c5a81..ae0995341a78 100644
> >>> --- a/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
> >>> +++ b/Documentation/devicetree/bindings/interconnect/qcom,osm-l3.yaml
> >>> @@ -16,13 +16,21 @@ description:
> >>>  
> >>>  properties:
> >>>    compatible:
> >>> -    enum:
> >>> -      - qcom,sc7180-osm-l3
> >>> -      - qcom,sc7280-epss-l3
> >>> -      - qcom,sc8180x-osm-l3
> >>> -      - qcom,sdm845-osm-l3
> >>> -      - qcom,sm8150-osm-l3
> >>> -      - qcom,sm8250-epss-l3
> >>> +    oneOf:
> >>> +      items:
> >>
> >> oneOf expects a list, so this should be "    - items"
> >>
> > 
> > Ahh, thanks. Must have missed running the dt_binding_check on this one.
> > 
> >>> +        - enum:
> >>> +            - qcom,sc7180-osm-l3
> >>> +            - qcom,sc8180x-osm-l3
> >>> +            - qcom,sdm845-osm-l3
> >>> +            - qcom,sm8150-osm-l3
> >>> +        - const: qcom,osm-l3
> >>
> >> The concept is good, but are you sure all SoCs will be compatible with
> >> generic osm-l3?
> > 
> > Per the current implementation yes, worst case if one or more of them isn't the
> > more specific compatible can be used to alter the behavior of that platform.
> > 
> >> Why not using dedicated compatible of one soc, e.g. the
> >> oldest here? We already did like that for BWMON, DMA and few others.
> >>
> > 
> > Because if we say compatible = "qcom,sc8180x-osm-l3", "qcom,sdm845-osm-l3" and
> > there is a quirk needed for "qcom,sdm845-osm-l3" we're forced to add a "special
> > case" every other *-osm-l3 in the driver.
> > 
> > This way we can have a generic implementation for the qcom,osm-l3 and if we
> > realize that we need to quirk something for the oldest platform, we can do so
> > without affecting the others.
> 
> True. This also means we do not really know which one is the generic
> implementation :)
> 

There currently is an implementation without platform specific quirks, I
call that the generic implementation and suggest that we refer to that
using "qcom,osm-l3".

If we instead were to use sdm845 as the generic compatible, and there
turns out to be a need for a quirk for this platform, you:

1) no longer have a generic implementation, but 4 platform-specific
   implementations

2) have 3 platforms claiming to be compatible with the quirked (now
   specialized) implementation, which they clearly aren't anymore

Therefor I favor using generic names for generic compatibles.

Regards,
Bjorn