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

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Message-ID: <b1b33000-4c10-43cd-bcf4-d24fc73902b1@lunn.ch>
Date: Wed, 9 Apr 2025 16:04:51 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Cc: Herve Codina <herve.codina@...tlin.com>,
	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 <dragan.cvetic@....com>,
	Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mark Brown <broonie@...nel.org>, Len Brown <lenb@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sakari Ailus <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,
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	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>
Subject: Re: [PATCH 15/16] misc: lan966x_pci: Add dtso nodes in order to
 support SFPs

On Wed, Apr 09, 2025 at 09:44:25AM +0200, Thomas Petazzoni wrote:
> On Tue Apr 8, 2025 at 5:38 PM CEST, Andrew Lunn wrote:
> 
> > "HW blocks inside an SoC." That would be the SoC .dtsi file. Anything
> > outside of the SoC is in the .dts file. OEM vendors take the SoC,
> > build a board around it, and name there .dts file after the board,
> > describing how the board components are connected to the SoC.
> >
> > So..
> >
> > So by PCI endpoint, you mean the PCIe chip? So it sounds like there
> > should be a .dtsi file describing the chip.
> >
> > Everything outside of the chip, like the SFP cages, are up to the
> > vendor building the board. I would say that should be described in a
> > .dtso file, which describes how the board components are connected to
> > the PCIe chip? And that .dtso file should be named after the board,
> > since there are going to many of them, from different OEM vendors.
> 
> Indeed, that makes sense. So if I get correctly your suggestion,
> instead of having a .dtso that describes everything, it should be
> split between:
> 
>  - A .dtsi that describes what's inside the LAN996x when used in PCI
>    endpoint mode
> 
>  - A .dtso that includes the above .dtsi, and that describes what on
>    the PCI board around the LAN966x.
> 
> Correct?

Yes.

And you need some way to map the PCI ID to the correct .dtso file.
Maybe that is just a lookup table in the driver, or maybe you can pack
the .dtso file into a kernel module with the correct
MODULE_DEVICE_TABLE(pci, ...) so that PCI probing pulls in the
specific driver module with the .dtso, which via dependencies pulls in
the core driver which can actually make use of the .dtso?

    Andrew