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Date: Sat, 04 Apr 2026 00:21:26 +0200
From: Nicolai Buchwitz <nb@tipi-net.de>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Thomas Richard <thomas.richard@bootlin.com>, Andrew Lunn
 <andrew+netdev@lunn.ch>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Rob Herring
 <robh@kernel.org>, Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley
 <conor+dt@kernel.org>, Aaro Koskinen <aaro.koskinen@iki.fi>, Andreas Kemnade
 <andreas@kemnade.info>, Kevin Hilman <khilman@baylibre.com>, Roger Quadros
 <rogerq@kernel.org>, Tony Lindgren <tony@atomide.com>, Thomas Petazzoni
 <thomas.petazzoni@bootlin.com>, netdev@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-omap@vger.kernel.org
Subject: Re: [PATCH 0/2] Add USB Ethernet controller (LAN7500) node in
 VAR-SOM-OM44 devicetree
In-Reply-To: <20260403151500.5225681d@kernel.org>
References: <20260403-b4-var-som-om44-lan7500-v1-0-0dadde850143@bootlin.com>
 <20260403131801.359be561@kernel.org>
 <2f843cc38fce1c5df9291c2e4b064241@tipi-net.de>
 <20260403151500.5225681d@kernel.org>
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On 4.4.2026 00:15, Jakub Kicinski wrote:
> On Fri, 03 Apr 2026 22:33:26 +0200 Nicolai Buchwitz wrote:
>> On 3.4.2026 22:18, Jakub Kicinski wrote:
>> > On Fri, 03 Apr 2026 21:02:22 +0200 Thomas Richard wrote:
>> >> The goal of this series is to add the USB Ethernet controller node in
>> >> the
>> >> VAR-SOM-OM44 devicetree in order to allow the bootloader to patch the
>> >> devicetree and pass a MAC address to the smsc75xx driver. This was
>> >> also a
>> >> good opportunity to create the schema file for LAN75XX devices.
>> >
>> > But there's no driver for it yet, right?
>> > IDK what the best practices are here, just unusual to see a schema
>> > without a driver, is all.
>> 
>> The smsc75xx driver has been in the tree since 2010 (d0cad871703b) and
>> already reads local-mac-address/mac-address from devicetree via
>> platform_get_ethdev_address() in smsc75xx_init_mac_address(), so the
>> binding should be covered on the driver side.
> 
> Curious. So USB core can tie the right USB device to the DT / OF
> information automatically? I was thrown by the fact that there
> are no matches on the compatibles anywhere in the kernel.

Yes, USB core matches DT nodes by port topology (reg property), not by
compatible (usb_of_get_device_node() in drivers/usb/core/of.c if you
want to have a deeper look).

The existing microchip,lan95xx.yaml binding works the same way.
For example Raspberry Pi models before the Pi 4 use exactly this
pattern to pass the MAC address via firmware -> devicetree to the
smsc95xx driver.