linux-kernel - Re: [PATCH v3 2/4] dt-bindings: mips: brcm: Document brcm,bmips-cbr-reg property

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Date: Thu, 9 May 2024 09:01:56 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Christian Marangi <ansuelsmth@...il.com>, Conor Dooley <conor@...nel.org>
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>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, linux-mips@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] dt-bindings: mips: brcm: Document
 brcm,bmips-cbr-reg property

On 5/8/24 10:17, Christian Marangi wrote:
> On Wed, May 08, 2024 at 06:14:34PM +0100, Conor Dooley wrote:
>> On Wed, May 08, 2024 at 07:07:18PM +0200, Christian Marangi wrote:
>>> Document brcm,bmips-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.
>>>
>>> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
>>> ---
>>>   .../devicetree/bindings/mips/brcm/soc.yaml    | 23 +++++++++++++++++++
>>>   1 file changed, 23 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mips/brcm/soc.yaml b/Documentation/devicetree/bindings/mips/brcm/soc.yaml
>>> index 975945ca2888..77f73ab48c11 100644
>>> --- a/Documentation/devicetree/bindings/mips/brcm/soc.yaml
>>> +++ b/Documentation/devicetree/bindings/mips/brcm/soc.yaml
>>> @@ -55,6 +55,15 @@ properties:
>>>            under the "cpus" node.
>>>           $ref: /schemas/types.yaml#/definitions/uint32
>>>   
>>> +      brcm,bmips-cbr-reg:
>>> +        description: Reference address of the CBR.
>>
>> Pretty sure that Rob commented last time that there's no definition
>> anywhere here of CBR, but I don't see either a response to him or an
>> explanation in v3 as to what CBR means.
>>
> 
> Sorry I missed it.

FWIW, CBR mean Core Base Register. It is accessed via co-processor 0, 
register 22, selector 6 using the MIPS processor's way of adding custom 
co-processor registers.
-- 
Florian


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