linux-kernel - Re: [PATCH 15/16] misc: lan966x_pci: Add dtso nodes in order to support SFPs

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Message-Id: <D91CSNC07NYM.3KC467K0OZ4GG@bootlin.com>
Date: Tue, 08 Apr 2025 17:13:54 +0200
From: "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>
To: "Herve Codina" <herve.codina@...tlin.com>, "Andrew Lunn"
 <andrew@...n.ch>
Cc: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, "Danilo Krummrich" <dakr@...nel.org>, "Shawn Guo"
 <shawnguo@...nel.org>, "Sascha Hauer" <s.hauer@...gutronix.de>,
 "Pengutronix Kernel Team" <kernel@...gutronix.de>, "Fabio Estevam"
 <festevam@...il.com>, "Michael Turquette" <mturquette@...libre.com>,
 "Stephen Boyd" <sboyd@...nel.org>, "Andi Shyti" <andi.shyti@...nel.org>,
 "Wolfram Sang" <wsa+renesas@...g-engineering.com>, "Peter Rosin"
 <peda@...ntia.se>, "Derek Kiernan" <derek.kiernan@....com>, "Dragan Cvetic"
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 <andriy.shevchenko@...ux.intel.com>, "Daniel Scally" <djrscally@...il.com>,
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 <sakari.ailus@...ux.intel.com>, "Wolfram Sang" <wsa@...nel.org>, "Geert
 Uytterhoeven" <geert+renesas@...der.be>, <linux-kernel@...r.kernel.org>,
 <imx@...ts.linux.dev>, <linux-arm-kernel@...ts.infradead.org>,
 <linux-clk@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-pci@...r.kernel.org>,
 <linux-spi@...r.kernel.org>, <linux-acpi@...r.kernel.org>, "Allan Nielsen"
 <allan.nielsen@...rochip.com>, "Horatiu Vultur"
 <horatiu.vultur@...rochip.com>, "Steen Hegelund"
 <steen.hegelund@...rochip.com>, "Luca Ceresoli"
 <luca.ceresoli@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 15/16] misc: lan966x_pci: Add dtso nodes in order to
 support SFPs

Andrew, Hervé,

On Tue Apr 8, 2025 at 4:26 PM CEST, Herve Codina wrote:

>> What exactly does this DTSO file represent?
>
> The dsto represents de board connected to the PCI slot and identified
> by its PCI vendor/device IDs.

If I may extend on that by providing what I believe is a more
accurate/precise definition.

The DTSO doesn't represent the board, rather it describes the HW
topology of the devices inside the PCI endpoint. Indeed, the PCI
endpoint is a full-blown SoC with lots of different HW blocks that
already have drivers in the kernel (because the same chip can be used
with Linux running on an ARM core embedded in the SoC, rather than
access as a PCI endpoint). So the DTSO describes the full topology of
the HW blocks inside this complex PCI endpoint, just like the DTS
describes the full topology of the HW blocks inside an SoC.

Please see:

  https://lpc.events/event/17/contributions/1421/attachments/1337/2680/LPC2023%20Non-discoverable%20devices%20in%20PCI.pdf

And most notably slide 6.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com