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

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Message-ID: <CAPqJEFqN-13MyDaCPV31RJjrgmXkx=pTVmgZ6KhabY3xTP6kxg@mail.gmail.com>
Date:   Thu, 20 Jul 2023 18:16:19 +0800
From:   Eric Lin <eric.lin@...ive.com>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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>
Subject: Re: [PATCH 3/3] dt-bindings: riscv: sifive: Add SiFive Private L2
 cache controller

Hi Conor,

On Wed, Jul 12, 2023 at 8:49 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> On Wed, Jul 12, 2023 at 02:30:06PM +0200, Krzysztof Kozlowski wrote:
> > 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.
> > >>
> > > 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?
>
> I probably should've been keeping a closer eye here, sorry.
>
> I assume what Krzysztof means is why do you permit both
> "sifive,pL2Cache0" and "sifive,pL2Cache1" appearing in isolation. IOW,
> both of
> compatible = "sifive,pl2cache0";
> and
> compatible = "sifive,pl2cache1";
> are valid in your binding.
>
> The hardware for both might be different, and their full featuresets may
> be incompatible, but they implement a compatible subset of features. I
> would expect that the following would be the permitted compatible setups:
> compatible = "sifive,pl2cache0";
> and
> compatible = "sifive,pl2cache1", "sifive,pl2cache0";
>
> A consumer of the DT that does care for the differences should be
> looking for the specific compatible, and OS code that does not care can
> always bind to the "0" version.
>

Yes, but I think the proper compatible string for hw pl2cache0 and hw
pl2cache1 should be as follows:
hw pl2cache0 -> compatible = "sifive,pl2cache0","sifive,pl2cache1";
hw pl2cache1 -> compatible = "sifive,pl2cache1";

Since the hw pl2cache0 implements more features than hw pl2cache1, it
can be compatible with the pl2cache1 driver.
However, hw pl2cache1 only implements a sub-feature of hw pl2cache0,
so it cannot be compatible with the pl2cache0 driver.
Thus, I'll keep only the compatible = "sifive,pl2cache1". in the
driver and dt-binding.  Thanks for the suggestions.

> Do the "0" & "1" here refer to the IP version, as in
> sifive-blocks-ip-versioning.txt? I didn't think the compatibles
> containing those IP versions were supposed to appear in isolation,
> without a soc-specific one?
>
Yes, I think they refer to IP versions. OK, I'll fix it in v2.
Thanks for the review.

Best regards,
Eric Lin

> Thanks,
> Conor.