linux-kernel - Re: [PATCH 3/4] dt-bindings: soc: samsung: exynos-sysreg: add dedicated SYSREG compatibles to Exynos5433

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Date:   Fri, 25 Nov 2022 16:01:25 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sam Protsenko <semen.protsenko@...aro.org>
Cc:     Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org,
        Sriranjani P <sriranjani.p@...sung.com>,
        Chanho Park <chanho61.park@...sung.com>
Subject: Re: [PATCH 3/4] dt-bindings: soc: samsung: exynos-sysreg: add
 dedicated SYSREG compatibles to Exynos5433

On 25/11/2022 15:57, Sam Protsenko wrote:
> On Fri, 25 Nov 2022 at 08:47, Krzysztof Kozlowski
> <krzysztof.kozlowski@...aro.org> wrote:
>>
>> On 25/11/2022 15:22, Sam Protsenko wrote:
>>> On Fri, 25 Nov 2022 at 05:22, Krzysztof Kozlowski
>>> <krzysztof.kozlowski@...aro.org> wrote:
>>>>
>>>> Exynos5433 has several different SYSREGs, so use dedicated compatibles
>>>> for them.
>>>>
>>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>>>
>>>> ---
>>>>
>>>> Cc: Sriranjani P <sriranjani.p@...sung.com>
>>>> Cc: Chanho Park <chanho61.park@...sung.com>
>>>> Cc: Sam Protsenko <semen.protsenko@...aro.org>
>>>> ---
>>>
>>> Hi Krzysztof,
>>>
>>> Just curious: what is the rationale for adding those more specific
>>> sysregs? AFAIR, e.g. in Exynos850, different SysReg instances have
>>> pretty much the same register layout.
>>>
>>
>> On Exynos5433 all these blocks have different registers. Are you saying
>> that Exynos850 has four (or more) sysregs which are exactly the same?
>> Same registers? Why would they duplicate it?
>>
> 
> Ah, no, you are right. Just checked it, they are different. Just first
> couple of registers are similar between blocks, that's why I memorized
> it wrong.
> 
> So as I understand, adding those new compatibles follows "describe HW,
> not a driver" rule? Because AFAIU, right now it'll fallback to
> "syscon" compatible anyway.

Yes, they describe hardware. Of course all of these sysregs are similar
as they are just bunch of SFR/MMIO-region, but they have different
roles/features. For example some other devices (users) of syscon/sysreg
should reference specific device, not any sysreg.

On several other architectures we use specific compatibles, so I think
for Samsung we should do the same.

Different case was for Exynos 3/4/5 where there was only one SYSREG.

Best regards,
Krzysztof