linux-kernel - Re: [PATCH v6 00/10] Add support for RaspberryPi RP1 PCI device using a DT overlay

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Message-ID: <CAMEGJJ3-JXhin_Ht76EqUNAwLiNisa9PrCrdUzCgj=msGZfb5A@mail.gmail.com>
Date: Thu, 13 Feb 2025 16:30:44 +0000
From: Phil Elwell <phil@...pberrypi.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Herve Codina <herve.codina@...tlin.com>, Andrea della Porta <andrea.porta@...e.com>, 
	Arnd Bergmann <arnd@...db.de>, 
	"maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" <bcm-kernel-feedback-list@...adcom.com>, bhelgaas@...gle.com, brgl@...ev.pl, 
	Catalin Marinas <catalin.marinas@....com>, Conor Dooley <conor+dt@...nel.org>, derek.kiernan@....com, 
	devicetree@...r.kernel.org, dragan.cvetic@....com, 
	Florian Fainelli <florian.fainelli@...adcom.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, krzk+dt@...nel.org, kw@...ux.com, 
	Linus Walleij <linus.walleij@...aro.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, linux-clk@...r.kernel.org, 
	linux-gpio@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, 
	"open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" <linux-pci@...r.kernel.org>, 
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-rpi-kernel@...ts.infradead.org>, lpieralisi@...nel.org, 
	luca.ceresoli@...tlin.com, manivannan.sadhasivam@...aro.org, 
	masahiroy@...nel.org, Michael Turquette <mturquette@...libre.com>, 
	Rob Herring <robh@...nel.org>, saravanak@...gle.com, Stephen Boyd <sboyd@...nel.org>, 
	thomas.petazzoni@...tlin.com, Stefan Wahren <wahrenst@....net>, 
	Will Deacon <will@...nel.org>, Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v6 00/10] Add support for RaspberryPi RP1 PCI device using
 a DT overlay

Hi Andrew,

On Thu, 13 Feb 2025 at 16:27, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Thu, Feb 13, 2025 at 05:14:35PM +0100, Herve Codina wrote:
> > Hi Phil,
> >
> > On Thu, 13 Feb 2025 15:18:45 +0000
> > Phil Elwell <phil@...pberrypi.com> wrote:
> >
> > > Hi Andrea,
> > >
> > > The problem with this approach (loading an overlay from the RP1 PCIe
> > > driver), and it's one that I have raised with you offline, is that
> > > (unless anyone can prove otherwise) it becomes impossible to create a
> > > Pi 5 DTS file which makes use of the RP1's resources. How do you
> > > declare something as simple as a button wired to an RP1 GPIO, or fan
> > > connected to a PWM output?
>
> Where is this button or fan? On a pluggable board? Isn't that what
> overlays are for, and they are stackable. So when you probe the
> pluggable board via its eeprom etc, you find the overlay and load it?

In the Raspberry Pi ecosystem it would be the firmware that applies
the overlay, and it can't do that if the resources the overlay refers
to are not yet present in the dtb.

> Or do you mean a custom board, which has a CPU, RP1 and the button and
> fan are directly on this custom board? You then want a board DTS which
> includes all these pieces?

That depends on whether you count the Raspberry Pi 5 as a custom board.

Phil