linux-kernel - Re: [net-next RFC PATCH 03/14] dt-bindings: net: document ethernet PHY package nodes

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Message-ID: <20231124194016.tcmu4w2r7jrnv6mo@skbuf>
Date:   Fri, 24 Nov 2023 21:40:16 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Christian Marangi <ansuelsmth@...il.com>,
        Rob Herring <robh@...nel.org>,
        "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>,
        Conor Dooley <conor+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Daniel Golle <daniel@...rotopia.org>,
        Qingfang Deng <dqfext@...il.com>,
        SkyLake Huang <SkyLake.Huang@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        David Epping <david.epping@...singlinkelectronics.com>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Harini Katakam <harini.katakam@....com>,
        Simon Horman <horms@...nel.org>,
        Robert Marko <robert.marko@...tura.hr>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [net-next RFC PATCH 03/14] dt-bindings: net: document ethernet
 PHY package nodes

On Fri, Nov 24, 2023 at 07:35:35PM +0100, Andrew Lunn wrote:
> > I think you are hitting some of the same points I have hit with DSA.
> > The PHY package could be considered an SoC with lots of peripherals on
> > it, for which you'd want separate drivers.
> 
> At least at the moment, this is not true. The package does just
> contain PHYs. But it also has some properties which are shared across
> those PHYs, e.g. reset. 
> 
> What you describe might become true in the future. e.g. The LED/GPIO
> controller is currently part of the PHY, and each PHY has its own. I
> could however imagine that becomes a block of its own, outside of the
> PHY address space, and maybe it might want its own class LED
> driver. Some PHYs have temperature sensors, which could be a package
> sensor, so could in theory be an individual hwmon driver. However,
> i've not yet seen such a package.
> 
> Do we consider this now? At the moment i don't see an MFD style system
> is required. We could crystal ball gaze and come up with some
> requirements, but i would prefer to have some real devices and
> datasheets. Without them, we will get the requirements wrong.
> 
> I also think we are not that far away from it, in terms of DT, if you
> consider the later comments. I suggested we need a phy package
> specific compatible. At the moment, it will be ignored by the kernel,
> the kernel does not need it, it probes the PHYs in the current way,
> using the ID registers. But it could in future be used to probe a real
> driver, which could be an MFD style driver. We need to see updated DT
> binding examples, but i don't see why we cannot slot it in at a later
> date.

I'm not suggesting to go for MFD right away. Just with a structure that
is extensible to possibly cover that. For now, a package node with a
Qualcomm compatible, with the most minimal driver that forwards MDIO
access to PHY children.

I can't speak for the future of PHY drivers, since I don't know enough
about PHYs. I'm just coming from the DSA background where I really wish
we had this sort of infrastructure earlier. Now I have the SJA1110 which
still lacks support for the interrupt controller for its integrated
PHYs, and a bunch of other IP blocks in the package, because it's so
incredibly hard to make the driver support the old-style and the
new-style device trees.