linux-kernel - Re: [PATCH 1/5] dt-bindings: mips: Document mti,mips-cm

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Message-ID: <871pz5vom3.fsf@BLaptop.bootlin.com>
Date: Wed, 20 Nov 2024 17:47:32 +0100
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Rob Herring <robh@...nel.org>
Cc: Aleksandar Rikalo <arikalo@...il.com>, Thomas Bogendoerfer
 <tsbogend@...ha.franken.de>, Jiaxun Yang <jiaxun.yang@...goat.com>,
 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,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] dt-bindings: mips: Document mti,mips-cm

Rob Herring <robh@...nel.org> writes:

> On Fri, Nov 15, 2024 at 04:29:54PM +0100, Gregory CLEMENT wrote:
>> From: Jiaxun Yang <jiaxun.yang@...goat.com>
>> 
>> Add devicetree binding documentation for MIPS Coherence Manager.
>> 
>> gc: reg is no more mandatory
>
> The h/w either has registers or it doesn't. Can't be both ways.

The register addresses are retrieved dynamically on most
hardware. However, for some of them, retrieval was broken, requiring it
to pass through the device tree. This was the initial purpose behind
introducing this binding. In the eyequ6 case, we have a hardware issue
in a different way; the address registers are correct, but the Hardware
Cache Instruction is broken. As such, we do not want to provide a
register address, instead, notifying about this issue through a property
or compatible string.

That's the reason why I want to make the register optional; however, if
I use a dedicated compatible string, then I can just remove the 'reg'
property for this binding.

Gregory

>
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>> Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>
>> ---
>>  .../devicetree/bindings/mips/mti,mips-cm.yaml      | 37 ++++++++++++++++++++++
>>  1 file changed, 37 insertions(+)
>> 
>> diff --git a/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml b/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..03a5ba5624a429c428ee2afca73b3e29127e02f9
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/mips/mti,mips-cm.yaml
>> @@ -0,0 +1,37 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/mips/mti,mips-cm.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: MIPS Coherence Manager
>> +
>> +description: |
>
> Don't need '|' if no formatting to preserve.
>
>> +  Defines a location of the MIPS Coherence Manager registers.
>> +
>> +maintainers:
>> +  - Jiaxun Yang <jiaxun.yang@...goat.com>
>> +
>> +properties:
>> +  compatible:
>> +    const: mti,mips-cm
>> +
>> +  reg:
>> +    description:
>> +      Base address and size of an unoccupied region in system's MMIO address
>> +      space, which will be used to map the MIPS CM global control registers
>> +      block. It is conventionally decided by the system integrator.
>> +    maxItems: 1
>> +
>> +required:
>> +  - compatible
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    coherency-manager@...f8000 {
>> +      compatible = "mti,mips-cm";
>> +      reg = <0x1bde8000 0x8000>;
>> +    };
>> +...
>> 
>> -- 
>> 2.45.2
>> 

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