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

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Message-ID: <20250213180733.11999e07@bootlin.com>
Date: Thu, 13 Feb 2025 18:07:33 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Phil Elwell <phil@...pberrypi.com>
Cc: Andrew Lunn <andrew@...n.ch>, 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

On Thu, 13 Feb 2025 16:30:44 +0000
Phil Elwell <phil@...pberrypi.com> wrote:

> 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.

What do you mean by the 'the resources are not yet present in the dtb' ?

Also what you call the 'firmware' is the bootloader ? the kernel ?
Can you tell me who is the 'firmware' what is the mecanisme it uses to
load the overlay.

Best regards,
Hervé


> 
> > 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.
>