linux-kernel - Re: [PATCH 3/3] dt-bindings: riscv: sifive: Add SiFive Private L2 cache controller

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Date:   Wed, 12 Jul 2023 14:30:06 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Eric Lin <eric.lin@...ive.com>
Cc:     conor@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, dslin1010@...il.com,
        Zong Li <zong.li@...ive.com>, vincent.chen@...ive.com,
        Greentime Hu <greentime.hu@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 3/3] dt-bindings: riscv: sifive: Add SiFive Private L2
 cache controller

On 12/07/2023 13:09, Eric Lin wrote:
> On Sat, Jul 01, 2023 at 10:22:25AM +0200, Krzysztof Kozlowski wrote:
>> On 28/06/2023 18:31, Eric Lin wrote:
>>
>>>>>>
>>>>>>> +      - enum:
>>>>>>> +          - sifive,pL2Cache0
>>>>>>> +          - sifive,pL2Cache1
>>>>>>
>>>>>> What is "0" and "1" here? What do these compatibles represent? Why they
>>>>>> do not have any SoC related part?
>>>>>
>>>>> The pL2Cache1 has minor changes in hardware, but it can use the same
>>>>> pl2 cache driver.
>>>>
>>>> Then why aren't they compatible?
>>>>
>>>
>>> The pL2Cache1 has removed some unused bits in the register compared to
>>> pl2Cache0.
>>> From the hardware perspective, they are not compatible but they can
>>> share the same pl2 cache driver in software.
>>
>> So they are compatible... If they were not compatible, you wouldn't be
>> able to use the same match in the driver.
>>
>>> Thus, we would like to keep both. It would be great if you can provide
>>> some suggestions. Thanks.
>>
>> I propose to make them compatible, like every other piece of SoC. I
>> don't see any benefit of having them separate.
>>
> 
> Hi Krzysztof,
> 
> Sorry for the late reply.
> The pl2 cache is our internal platform IP and is not part of any SoC. 
> 
> The reason why this driver is compatible with the hardware "pl2cache0" and hardware "pl2cache1"
> is that it doesn't program the different parts of the config register
> However, our internal software (e.g., bare-metal software) will program these different parts,
> so it needs to rely on the different compatible string to identify the hardware.
>   
> Additionally, we would like the compatible strings to reflect which hardware is being used Thanks.

I don't understand how does it contradicts anything I said. So you do
agree with me? Or what?

Best regards,
Krzysztof