linux-kernel - Re: [PATCH net-next 1/2] dt-bindings: net: lan966x: remove PHY reset

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Date:   Tue, 03 May 2022 15:22:32 +0200
From:   Michael Walle <michael@...le.cc>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        netdev <netdev@...r.kernel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] dt-bindings: net: lan966x: remove PHY reset

Am 2022-05-03 15:04, schrieb Rob Herring:
> On Thu, Apr 28, 2022 at 6:40 AM Michael Walle <michael@...le.cc> wrote:
>> 
>> The PHY reset was intended to be a phandle for a special PHY reset
>> driver for the integrated PHYs as well as any external PHYs. It turns
>> out, that the culprit is how the reset of the switch device is done.
>> In particular, the switch reset also affects other subsystems like
>> the GPIO and the SGPIO block and it happens to be the case that the
>> reset lines of the external PHYs are connected to a common GPIO line.
>> Thus as soon as the switch issues a reset during probe time, all the
>> external PHYs will go into reset because all the GPIO lines will
>> switch to input and the pull-down on that signal will take effect.
>> 
>> So even if there was a special PHY reset driver, it (1) won't fix
>> the root cause of the problem and (2) it won't fix all the other
>> consumers of GPIO lines which will also be reset.
>> 
>> It turns out, the Ocelot SoC has the same weird behavior (or the
>> lack of a dedicated switch reset) and there the problem is already
>> solved and all the bits and pieces are already there and this PHY
>> reset property isn't not needed at all.
>> 
>> There are no users of this binding. Just remove it.
> 
> Seems there was 1 user:
> 
> /builds/robherring/linux-dt/Documentation/devicetree/bindings/net/microchip,lan966x-switch.example.dtb:
> switch@...00000: resets: [[4294967295, 0], [4294967295, 0]] is too
> long
>  From schema:
> /builds/robherring/linux-dt/Documentation/devicetree/bindings/net/microchip,lan966x-switch.yaml
> /builds/robherring/linux-dt/Documentation/devicetree/bindings/net/microchip,lan966x-switch.example.dtb:
> switch@...00000: reset-names: ['switch', 'phy'] is too long
>  From schema:
> /builds/robherring/linux-dt/Documentation/devicetree/bindings/net/microchip,lan966x-switch.yaml
> 
> Please fix as this is now failing in linux-next.

Sorry. Should be fixed with
https://lore.kernel.org/netdev/20220503132038.2714128-1-michael@walle.cc/

-michael