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

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Message-ID: <20250213171435.1c2ce376@bootlin.com>
Date: Thu, 13 Feb 2025 17:14:35 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Phil Elwell <phil@...pberrypi.com>
Cc: Andrea della Porta <andrea.porta@...e.com>, andrew@...n.ch, 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 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?

The driver could be improved in a second step.
For instance, it could load the dtbo from user-space using request_firmare()
instead of loading the embedded dtbo.

> 
> If this is the preferred route to upstream adoption, I would prefer it
> if rp1.dtso could be split in two - an rp1.dtsi similar to what we
> have downstream, and an rp1.dtso that #includes it. In this way we can
> keep the patching and duplication to a minimum.

Indeed, having a rp1.dtsi avoid duplication but how the rp1.dtso in
the the kernel sources could include user customization (button, fan, ...)
without being modified ?
At least we have to '#include <my_rp1_customizations.dtsi>'.

Requesting the dtbo from user-space allows to let the user to create
its own dtso without the need to modify the one in kernel sources.

Does it make sense ?

Best regards,
Hervé