linux-kernel - Re: [Patch v3 1/2] dt-bindings: make sid and broadcast reg optional

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Message-Id: <D0T3R7UPFO07.2VR2436TG4N8B@gmail.com>
Date: Thu, 25 Apr 2024 11:39:44 +0200
From: "Thierry Reding" <thierry.reding@...il.com>
To: "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>, "Sumit Gupta"
 <sumitg@...dia.com>, <robh@...nel.org>, <conor+dt@...nel.org>,
 <maz@...nel.org>, <mark.rutland@....com>, <treding@...dia.com>,
 <jonathanh@...dia.com>
Cc: <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-tegra@...r.kernel.org>, <amhetre@...dia.com>, <bbasu@...dia.com>
Subject: Re: [Patch v3 1/2] dt-bindings: make sid and broadcast reg optional

On Thu Apr 25, 2024 at 9:52 AM CEST, Krzysztof Kozlowski wrote:
> On 24/04/2024 19:04, Thierry Reding wrote:
> > On Wed Apr 24, 2024 at 6:26 PM CEST, Thierry Reding wrote:
> >> On Mon Apr 22, 2024 at 9:02 AM CEST, Krzysztof Kozlowski wrote:
> >>> On 12/04/2024 15:05, Sumit Gupta wrote:
> >>>> MC SID and Broadbast channel register access is restricted for Guest VM.
> >>>
> >>> Broadcast
> >>>
> >>>> Make both the regions as optional for SoC's from Tegra186 onwards.
> >>>
> >>> onward?
> >>>
> >>>> Tegra MC driver will skip access to the restricted registers from Guest
> >>>> if the respective regions are not present in the memory-controller node
> >>>> of Guest DT.
> >>>>
> >>>> Suggested-by: Thierry Reding <treding@...dia.com>
> >>>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
> >>>> ---
> >>>>  .../nvidia,tegra186-mc.yaml                   | 95 ++++++++++---------
> >>>>  1 file changed, 49 insertions(+), 46 deletions(-)
> >>>>
> >>>> diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> >>>> index 935d63d181d9..e0bd013ecca3 100644
> >>>> --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> >>>> +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> >>>> @@ -34,11 +34,11 @@ properties:
> >>>>            - nvidia,tegra234-mc
> >>>>  
> >>>>    reg:
> >>>> -    minItems: 6
> >>>> +    minItems: 4
> >>>>      maxItems: 18
> >>>>  
> >>>>    reg-names:
> >>>> -    minItems: 6
> >>>> +    minItems: 4
> >>>>      maxItems: 18
> >>>>  
> >>>>    interrupts:
> >>>> @@ -151,12 +151,13 @@ allOf:
> >>>>  
> >>>>          reg-names:
> >>>>            items:
> >>>> -            - const: sid
> >>>> -            - const: broadcast
> >>>> -            - const: ch0
> >>>> -            - const: ch1
> >>>> -            - const: ch2
> >>>> -            - const: ch3
> >>>> +            enum:
> >>>> +              - sid
> >>>> +              - broadcast
> >>>> +              - ch0
> >>>> +              - ch1
> >>>> +              - ch2
> >>>> +              - ch3
> >>>
> >>> I understand why sid and broadcast are becoming optional, but why order
> >>> of the rest is now fully flexible?
> >>
> >> The reason why the order of the rest doesn't matter is because we have
> >> both reg and reg-names properties and so the order in which they appear
> >> in the list doesn't matter. The only thing that matters is that the
> >> entries of the reg and reg-names properties match.
> >>
> >>> This does not even make sid/broadcast optional, but ch0!
> >>
> >> Yeah, this ends up making all entries optional, which isn't what we
> >> want. I don't know of a way to accurately express this in json-schema,
> >> though. Do you?
> >>
> >> If not, then maybe we need to resort to something like this and also
> >> mention explicitly in some comment that it is sid and broadcast that are
> >> optional.
> > 
> > Actually, here's another variant that is a bit closer to what we want:
> > 
> > --- >8 ---
> > diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> > index 935d63d181d9..86f1475926e4 100644
> > --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> > +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
> > @@ -34,11 +34,11 @@ properties:
> >            - nvidia,tegra234-mc
> >  
> >    reg:
> > -    minItems: 6
> > +    minItems: 4
> >      maxItems: 18
> >  
> >    reg-names:
> > -    minItems: 6
> > +    minItems: 4
> >      maxItems: 18
> >  
> >    interrupts:
> > @@ -146,17 +146,21 @@ allOf:
> >      then:
> >        properties:
> >          reg:
> > +          minItems: 4
> >            maxItems: 6
> >            description: 5 memory controller channels and 1 for stream-id registers
> >  
> >          reg-names:
> > -          items:
> > -            - const: sid
> > -            - const: broadcast
> > -            - const: ch0
> > -            - const: ch1
> > -            - const: ch2
> > -            - const: ch3
> > +          anyOf:
> > +            - items:
> > +                enum: [ sid, broadcast, ch0, ch1, ch2, ch3 ]
> > +              uniqueItems: true
> > +              minItems: 6
> > +
> > +            - items:
> > +                enum: [ ch0, ch1, ch2, ch3 ]
> > +              uniqueItems: true
> > +              minItems: 4
> >  
> >    - if:
> >        properties:
> > @@ -165,29 +169,22 @@ allOf:
> >      then:
> >        properties:
> >          reg:
> > -          minItems: 18
> > +          minItems: 16
> >            description: 17 memory controller channels and 1 for stream-id registers
> >  
> >          reg-names:
> > -          items:
> > -            - const: sid
> > -            - const: broadcast
> > -            - const: ch0
> > -            - const: ch1
> > -            - const: ch2
> > -            - const: ch3
> > -            - const: ch4
> > -            - const: ch5
> > -            - const: ch6
> > -            - const: ch7
> > -            - const: ch8
> > -            - const: ch9
> > -            - const: ch10
> > -            - const: ch11
> > -            - const: ch12
> > -            - const: ch13
> > -            - const: ch14
> > -            - const: ch15
> > +          anyOf:
> > +            - items:
> > +                enum: [ sid, broadcast, ch0, ch1, ch2, ch3, ch4, ch5, ch6, ch7,
> > +                        ch8, ch9, ch10, ch11, ch12, ch13, ch14, ch15 ]
> > +              minItems: 18
> > +              uniqueItems: true
> > +
> > +            - items:
> > +                enum: [ ch0, ch1, ch2, ch3, ch4, ch5, ch6, ch7, ch8, ch9, ch10,
> > +                        ch11, ch12, ch13, ch14, ch15 ]
> > +              minItems: 16
> > +              uniqueItems: true
>
> No, because order is strict.

Why? I realize that prior to this the order was indeed strict and it's
common to have these listed in strict order in the DTS files. However,
this is an arbitrary restriction that was introduced in the patch that
added reg-names. However, */*-names properties have always assumed the
ordering to be non-strict because each entry from the * property gets
matched up with the corresponding entry in the *-names property, so the
ordering is completely irrelevant.

Thierry

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