linux-kernel - Re: [PATCH v2 01/12] dt-bindings: net: snps,dwmac: Allow exclusive usage of ahb reset

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Message-ID: <f3b66f3a-50a2-4c1b-830b-ad6d87b471e5@collabora.com>
Date:   Tue, 31 Oct 2023 13:00:59 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Samin Guo <samin.guo@...rfivetech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Richard Cochran <richardcochran@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v2 01/12] dt-bindings: net: snps,dwmac: Allow exclusive
 usage of ahb reset

On 10/31/23 07:48, Krzysztof Kozlowski wrote:
> On 30/10/2023 20:07, Cristian Ciocaltea wrote:
>> On 10/30/23 09:26, Krzysztof Kozlowski wrote:
>>> On 29/10/2023 23:24, Cristian Ciocaltea wrote:
>>>> On 10/29/23 13:25, Krzysztof Kozlowski wrote:
>>>>> On 29/10/2023 05:27, Cristian Ciocaltea wrote:
>>>>>> The Synopsys DesignWare MAC found on the StarFive JH7100 SoC requires
>>>>>> just the 'ahb' reset name, but the binding allows selecting it only in
>>>>>> conjunction with 'stmmaceth'.
>>>>>>
>>>>>> Fix the issue by permitting exclusive usage of the 'ahb' reset name.
>>>>>>
>>>>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>>>>>> ---
>>>>>>  Documentation/devicetree/bindings/net/snps,dwmac.yaml | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/net/snps,dwmac.yaml b/Documentation/devicetree/bindings/net/snps,dwmac.yaml
>>>>>> index 5c2769dc689a..a4d7172ea701 100644
>>>>>> --- a/Documentation/devicetree/bindings/net/snps,dwmac.yaml
>>>>>> +++ b/Documentation/devicetree/bindings/net/snps,dwmac.yaml
>>>>>> @@ -146,7 +146,7 @@ properties:
>>>>>>    reset-names:
>>>>>>      minItems: 1
>>>>>>      items:
>>>>>> -      - const: stmmaceth
>>>>>> +      - enum: [stmmaceth, ahb]
>>>>>
>>>>> Also, this makes sense only with patch #4, so this should be squashed there.
>>>>
>>>> I added this as a separate patch since it changes the generic schema
>>>> which is included by many other bindings.  JH7100 just happens to be the
>>>> first use-case requiring this update.  But I can squash the patch if
>>>> that's not a good enough reason to keep it separately.
>>>
>>> If there is no single user of this, why changing this? I would even
>>> argue that it is not correct from existing bindings point of view -
>>> nothing allows and uses ahb as the only reset. Even the commit msg
>>> mentions your hardware from patch 4.
>>
>> Sorry, I'm not sure I follow. JH7100 is (or will be) the user of it and,
>> as a matter of fact, something similar has been done recently while
>> adding support for JH7110.
> 
> Every patch should stand on its own and at this point nothing uses it.
> We apply this patch #1 and we add dead code, unused case.
> 
>>
>> In particular, commit [1] changed this binding before the JH7110
>> compatible was introduced in a subsequent patch. On a closer look that
>> commit made a statement which is not entirely correct:
>>
>> "dwmac controller may require one (stmmaceth) or two (stmmaceth+ahb)
>> reset signals"
>>
>> That's because stmmaceth is also optional in dwmac's driver, hence the
>> correct message would have been:
>>
>> "[...] may require one (stmmaceth OR ahb) [...]"
> 
> Driver does not describe the hardware. The bindings do, so according to
> that description all supported hardware required MAC reset (stmmaceth).
> Otherwise please point me to any hardware which skips MAC reset and
> requires AHB reset instead (not future hardware, but current).

I might have found one (arch/arm/boot/dts/allwinner/sun6i-a31.dtsi):

    gmac: ethernet@...0000 {
        compatible = "allwinner,sun7i-a20-gmac";
        [...]
        resets = <&ccu RST_AHB1_EMAC>;
        reset-names = "stmmaceth";
        [...]
    };

It's possible the 'stmmaceth' naming has been used instead of 'ahb' just
to avoid updating the binding, but that's just an assumption looking at
RST_AHB1_EMAC.

I will proceed with the squash for v3.

Thanks for clarifying,
Cristian