linux-kernel - Re: [PATCH v3 2/5] dt-bindings: mips: mips-cm: Add a new compatible string for EyeQ6

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Message-ID: <87tt9iucu9.fsf@BLaptop.bootlin.com>
Date: Tue, 28 Jan 2025 17:23:26 +0100
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Jiaxun Yang <jiaxun.yang@...goat.com>, Rob Herring <robh@...nel.org>
Cc: Aleksandar Rikalo <arikalo@...il.com>, Thomas Bogendoerfer
 <tsbogend@...ha.franken.de>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Vladimir Kondratiev
 <vladimir.kondratiev@...ileye.com>, Théo Lebrun
 <theo.lebrun@...tlin.com>,
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, "linux-mips@...r.kernel.org"
 <linux-mips@...r.kernel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] dt-bindings: mips: mips-cm: Add a new compatible
 string for EyeQ6

> 在2025年1月27日一月 下午10:07，Rob Herring写道：
>> On Mon, Jan 27, 2025 at 3:43 PM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>>>
>>>
>>>
>>> 在2025年1月23日一月 上午11:01，Gregory CLEMENT写道：
>>> > The CM3.5 used on EyeQ6 reports that Hardware Cache Initialization is
>>> > complete, but in reality it's not the case. It also incorrectly
>>> > indicates that Hardware Cache Initialization is supported. This new
>>> > compatible string allows warning about this broken feature that cannot
>>> > be detected at runtime.
>>> >
>>> > Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>
>>> > ---
>>> >  Documentation/devicetree/bindings/mips/mti,mips-cm.yaml | 12 +++++++++++-
>>> >  1 file changed, 11 insertions(+), 1 deletion(-)
>>> >
>>> > diff --git a/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>>> > b/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>>> > index
>>> > 4324b2306535f1bf66c44b1f96be9094ee282041..d129d6382847768dc026336d8d2c7328b6b81f9b
>>> > 100644
>>> > --- a/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>>> > +++ b/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>>> > @@ -19,7 +19,12 @@ maintainers:
>>> >
>>> >  properties:
>>> >    compatible:
>>> > -    const: mti,mips-cm
>>> > +    oneOf:
>>> > +      - const: mti,mips-cm
>>> > +      - const: mobileye,eyeq6-cm
>>> > +        description:
>>> > +          On EyeQ6 the HCI (Hardware Cache Initialization) information for
>>> > +          the L2 cache in multi-cluster configuration is broken.
>>> >
>>> >    reg:
>>> >      description:
>>> > @@ -44,4 +49,9 @@ examples:
>>> >        compatible = "mti,mips-cm";
>>> >        reg = <0x1bde8000 0x8000>;
>>> >      };
>>> > +
>>> > +  - |
>>> > +    coherency-manager {
>>> > +      compatible = "mobileye,eyeq6-cm";
>>>
>>> I think “mobileye,eyeq6-cm”, “mti,mips-cm” would describe the hardware better as eyeq6’s CM is just a special variant of mips-cm.
>>
>> Is s/w that only understands “mti,mips-cm” useful on eyeq6 chip? If
>> so, I agree. If not, then a fallback compatible is not useful.
>
> Yes, mobileye,eyeq6-cm only enable an additional bug workaround in software.
>

Having "mti,mips-cm" is not useful for the EyeQ6 chip. On the EyeQ6, we
obtain all relevant information related to CM dynamically without
needing this compatible string.

> The programming interfaces and so on remains unchanged.

Even without a compatible string, we are able to utilize the CM. At
present, there is no node in the device tree, and apart from the
hardware being faulty, we do not need it.

>
> Also other firmware components like U-Boot doesn’t need to be aware of
> eyeq6 variant.

It's the same for the firmware; they don't need to have "mti, mips-cm"
information, as they can retrieve all they need dynamically.

Gregory

-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com