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

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Message-ID: <20230712110908.GA23216@hsinchu16>
Date:   Wed, 12 Jul 2023 19:09:43 +0800
From:   Eric Lin <eric.lin@...ive.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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 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.

Best regards,
Eric Lin

> Best regards,
> Krzysztof
>