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

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Message-ID: <CAMdYzYrG8bK-Yo15RjhhCQKS4ZQW53ePu1q4gbGxVVNKPJHBWg@mail.gmail.com>
Date:   Sun, 8 May 2022 13:04:56 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     Frank Wunderlich <frank-w@...lic-files.de>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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: Re: [PATCH v3 5/6] dt-bindings: net: dsa: make reset optional and
 add rgmii-mode to mt7531

On Sun, May 8, 2022 at 8:12 AM Frank Wunderlich <frank-w@...lic-files.de> wrote:
>
> Hi Heiko
>
> > Gesendet: Sonntag, 08. Mai 2022 um 11:41 Uhr
> > Von: "Heiko Stuebner" <heiko@...ech.de>
> > Am Sonntag, 8. Mai 2022, 08:24:37 CEST schrieb Frank Wunderlich:
> > > Am 7. Mai 2022 22:01:22 MESZ schrieb Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>:
> > > >On 07/05/2022 19:04, Frank Wunderlich wrote:
> > > >> From: Frank Wunderlich <frank-w@...lic-files.de>
> > > >>
> > > >> Make reset optional as driver already supports it,
> > > >
> > > >I do not see the connection between hardware needing or not needing a
> > > >reset GPIO and a driver supporting it or not... What does it mean?
> > >
> > > My board has a shared gpio-reset between gmac and switch, so both will resetted if it
> > > is asserted. Currently it is set to the gmac and is aquired exclusive. Adding it to switch results in 2 problems:
> > >
> > > - due to exclusive and already mapped to gmac, switch driver exits as it cannot get the reset-gpio again.
> > > - if i drop the reset from gmac and add to switch, it resets the gmac and this takes too long for switch
> > > to get up. Of course i can increase the wait time after reset,but dropping reset here was the easier way.
> > >
> > > Using reset only on gmac side brings the switch up.
> >
> > 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 ;-) .
> >
> > 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
>
> 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.

>
> > > >> allow port 5 as
> > > >> cpu-port
> > > >
> > > >How do you allow it here?
> > >
> > > Argh, seems i accidentally removed this part and have not recognized while checking :(
> > >
> > > It should only change description of reg for ports to:
> > >
> > > "Port address described must be 5 or 6 for CPU port and from 0 to 5 for user ports."
>
> noticed that the target-phase is not removed but squashed in the first bindings-patch.
> This was a rebasing error and not intented...will fix in next version.
>
> regards Frank