linux-kernel - Re: [PATCH 3/6] dt-bindings: mips: brcm: Document mips-cbr-reg property

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Message-ID: <20240503-dreamboat-satin-4e51e27643b1@spud>
Date: Fri, 3 May 2024 23:14:10 +0100
From: Conor Dooley <conor@...nel.org>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Hauke Mehrtens <hauke@...ke-m.de>,
	Rafał Miłecki <zajec5@...il.com>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Álvaro Fernández Rojas <noltari@...il.com>,
	linux-mips@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Daniel González Cabanelas <dgcbueu@...il.com>
Subject: Re: [PATCH 3/6] dt-bindings: mips: brcm: Document mips-cbr-reg
 property

On Fri, May 03, 2024 at 09:33:35PM +0200, Christian Marangi wrote:
> On Fri, May 03, 2024 at 05:21:41PM +0100, Conor Dooley wrote:
> > On Fri, May 03, 2024 at 03:54:03PM +0200, Christian Marangi wrote:
> > > Document mips-cbr-reg and mips-broken-cbr-reg property.
> > > 
> > > Some SoC suffer from a BUG where read_c0_brcm_cbr() might return 0
> > > if called from TP1. The CBR address is always the same on the SoC
> > > hence it can be provided in DT to handle broken case where bootloader
> > > doesn't init it or SMP where read_c0_brcm_cbr() returns 0 from TP1.
> > > 
> > > Usage of this property is to give an address also in these broken
> > > configuration/bootloader.
> > > 
> > > If the SoC/Bootloader ALWAYS provide a broken CBR address the property
> > > "mips-broken-cbr-reg" can be used to ignore any value already set in the
> > > registers for CBR address.
> > > 
> > > Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> > > ---
> > >  .../devicetree/bindings/mips/brcm/soc.yaml    | 32 +++++++++++++++++++
> > >  1 file changed, 32 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/mips/brcm/soc.yaml b/Documentation/devicetree/bindings/mips/brcm/soc.yaml
> > > index 975945ca2888..12d394b7e011 100644
> > > --- a/Documentation/devicetree/bindings/mips/brcm/soc.yaml
> > > +++ b/Documentation/devicetree/bindings/mips/brcm/soc.yaml
> > > @@ -55,6 +55,21 @@ properties:
> > >           under the "cpus" node.
> > >          $ref: /schemas/types.yaml#/definitions/uint32
> > >  
> > > +      mips-broken-cbr-reg:
> > > +        description: Declare that the Bootloader init a broken
> > > +          CBR address in the registers and the one provided from
> > > +          DT should always be used.
> > 
> > Why is this property even needed, is it not sufficient to just add the
> > mips-cbr-reg property to the DT for SoCs that need it and use the
> > property when present?
> >
> 
> I described this in the cover letter.

It needs to be described in /this patch/. Cover letters usually don't
end up in the commit history and I din't read them while looking for the
justification for a change :)

> CBR might be set by the Bootloader
> and might be not 0. In that case the value is ignored as an extra
> precaution and the broken propetry is needed.

I dunno, if the bootloader is bad, you need to set a property anyway,
so why not set mips-cbr-reg?

> > > +        type: boolean
> > > +
> > > +      mips-cbr-reg:
> > 
> > Missing a vendor prefix.
> > 
> 
> I will change this to bmips,cbr-reg hope it's O.K.
> 
> > > +        description: Reference address of the CBR.
> > > +          Some SoC suffer from a BUG where read_c0_brcm_cbr() might
> > > +          return 0 if called from TP1. The CBR address is always the
> > > +          same on the SoC hence it can be provided in DT to handle
> > > +          broken case where bootloader doesn't init it or SMP where
> > 
> > s/init/initialise/ please :)
> > 
> 
> Sure!
> 
> > Thanks,
> > Conor.
> > 
> > > +          read_c0_brcm_cbr() returns 0 from TP1.
> > > +        $ref: /schemas/types.yaml#/definitions/uint32
> > > +
> > >      patternProperties:
> > >        "^cpu@[0-9]$":
> > >          type: object
> > > @@ -64,6 +79,23 @@ properties:
> > >      required:
> > >        - mips-hpt-frequency
> > >  
> > > +dependencies:
> > > +  mips-broken-cbr-reg: [ mips-cbr-reg ]
> > > +
> > > +if:
> > > +  properties:
> > > +    compatible:
> > > +      contains:
> > > +        anyOf:
> > > +          - const: brcm,bcm6358
> > > +          - const: brcm,bcm6368
> > > +
> > > +then:
> > > +  properties:
> > > +    cpus:
> > > +      required:
> > > +        - mips-cbr-reg
> > > +
> > >  additionalProperties: true
> > >  
> > >  examples:
> > > -- 
> > > 2.43.0
> > > 
> 
> 
> 
> -- 
> 	Ansuel

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