linux-kernel - Re: [PATCH v3 5/6] dt-bindings: net: dsa: make reset optional and add rgmii-mode to mt7531

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Date:   Mon, 9 May 2022 08:48:52 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Peter Geis <pgwipeout@...il.com>,
        Frank Wunderlich <frank-w@...lic-files.de>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Frank Wunderlich <linux@...web.de>,
        linux-mediatek@...ts.infradead.org, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Ungerer <gerg@...nel.org>,
        René van Dorst <opensource@...rst.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Subject: Re: [PATCH v3 5/6] dt-bindings: net: dsa: make reset optional and add
 rgmii-mode to mt7531

On 08/05/2022 19:04, Peter Geis wrote:
> On Sun, May 8, 2022 at 8:12 AM Frank Wunderlich <frank-w@...lic-files.de> wrote:
>>>
>>> I think the issue is more for the description itself.
>>>
>>> Devicetree is only meant to describe the hardware and does in general don't
>>> care how any firmware (Linux-kernel, *BSD, etc) handles it. So going with
>>> "the kernel does it this way" is not a valid reason for a binding change ;-) .

Exactly. The argument in commit msg was not matching the change, because
driver implementation should not be (mostly) a reason for such changes.

>>>
>>> Instead in general want to reason that there are boards without this reset
>>> facility and thus make it optional for those.
>>
>> if only the wording is the problem i try to rephrase it from hardware PoV.
>>
>> maybe something like this?
>>
>> https://github.com/frank-w/BPI-R2-4.14/commits/5.18-mt7531-mainline2/Documentation/devicetree/bindings/net/dsa/mediatek%2Cmt7530.yaml

Looks ok.

>>
>> Another way is maybe increasing the delay after the reset (to give more time all
>> come up again), but imho it is no good idea resetting the gmac/mdio-bus from the
>> child device.
>>
>> have not looked into the gmac driver if this always  does the initial reset to
>> have a "clean state". In this initial reset the switch will be resetted too
>> and does not need an additional one which needs the gmac/mdio initialization
>> to be done again.
> 
> For clarification, the reset gpio line is purely to reset the phy.
> If having the switch driver own the reset gpio instead of the gmac
> breaks initialization that means there's a bug in the gmac driver
> handling phy init.
> In testing I've seen issues moving the reset line to the mdio node
> with other phys and the stmmac gmac driver, so I do believe this is
> the case.

Yes, this seems reasonable, although Frank mentioned that reset is
shared with gmac, so it resets some part of it as well?




Best regards,
Krzysztof