netdev - Re: [PATCH net-next] ARM: dts: imx6qdl: Remove unnecessary mdio #address-cells/#size-cells

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Message-ID: <20210724170310.ylouwttmutkpin42@skbuf>
Date:   Sat, 24 Jul 2021 20:03:10 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Fabio Estevam <festevam@...il.com>, davem@...emloft.net,
        shawnguo@...nel.org, linux-arm-kernel@...ts.infradead.org,
        qiangqing.zhang@....com, robh+dt@...nel.org,
        netdev@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next] ARM: dts: imx6qdl: Remove unnecessary mdio
 #address-cells/#size-cells

On Sat, Jul 24, 2021 at 09:37:35AM -0700, Florian Fainelli wrote:
> On 7/23/2021 6:08 AM, Vladimir Oltean wrote:
> > Hi Fabio,
> >
> > On Fri, Jul 23, 2021 at 08:28:35AM -0300, Fabio Estevam wrote:
> > > Since commit dabb5db17c06 ("ARM: dts: imx6qdl: move phy properties into
> > > phy device node") the following W=1 dtc warnings are seen:
> > >
> > > arch/arm/boot/dts/imx6qdl-aristainetos2.dtsi:323.7-334.4: Warning (avoid_unnecessary_addr_size): /soc/bus@...0000/ethernet@...8000/mdio: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property
> > >
> > > Remove the unnecessary mdio #address-cells/#size-cells to fix it.
> > >
> > > Fixes: dabb5db17c06 ("ARM: dts: imx6qdl: move phy properties into phy device node")
> > > Signed-off-by: Fabio Estevam <festevam@...il.com>
> > > ---
> >
> > Are you actually sure this is the correct fix? If I look at mdio.yaml, I
> > think it is pretty clear that the "ethernet-phy" subnode of the MDIO
> > controller must have an "@[0-9a-f]+$" pattern, and a "reg" property. If
>
> It is valid to omit the "reg" property of an Ethernet PHY which the kernel
> will then dynamically scan for. If you know the Ethernet PHY address it's
> obviously better to set it so you avoid scanning and the time spent in doing
> that. The boot loader could (should?) also provide that information to the
> kernel for the same reasons.

Interesting, but brittle I suppose (it only works reliably with a single
PHY on a shared MDIO bus). NXP has "QDS" boards for internal development
and these have multi-port riser cards with various PHYs for various
SERDES protocols, and we have a really hard time describing the hardware
in DT (we currently use overlays applied by U-Boot), so we would like
some sort of auto-detection of PHYs if that was possible, but I think
that for anything except the simplest of cases it isn't. For example
what happens if you unbind and rebind two net devices in a different
order - they will connect to a PHY at a different address, won't they?

Anyway, I was wrong, ok, but I think the point still stands that
according to mdio.yaml this DT description is not valid. So after your
explanation, it is the DT schema that we should update.