linux-kernel - Re: [PATCH v8 08/13] misc: rp1: RaspberryPi RP1 misc driver

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Message-ID: <CAL_JsqJbdvMrUEVwp4_yC4efhwuK4eCLYWFpGdvrVcbr213aqg@mail.gmail.com>
Date: Tue, 15 Apr 2025 12:19:14 -0500
From: Rob Herring <robh@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Andrea della Porta <andrea.porta@...e.com>, Herve Codina <herve.codina@...tlin.com>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczynski <kw@...ux.com>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Linus Walleij <linus.walleij@...aro.org>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Bartosz Golaszewski <brgl@...ev.pl>, Derek Kiernan <derek.kiernan@....com>, 
	Dragan Cvetic <dragan.cvetic@....com>, Arnd Bergmann <arnd@...db.de>, 
	Saravana Kannan <saravanak@...gle.com>, linux-clk@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-gpio@...r.kernel.org, Masahiro Yamada <masahiroy@...nel.org>, 
	Stefan Wahren <wahrenst@....net>, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, Andrew Lunn <andrew@...n.ch>, 
	Phil Elwell <phil@...pberrypi.com>, Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	kernel-list@...pberrypi.com
Subject: Re: [PATCH v8 08/13] misc: rp1: RaspberryPi RP1 misc driver

On Tue, Apr 15, 2025 at 11:14 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Apr 15, 2025 at 05:41:26PM +0200, Andrea della Porta wrote:
> > Hi Greg,
> >
> > On 17:14 Tue 15 Apr     , Greg Kroah-Hartman wrote:
> > > On Tue, Apr 15, 2025 at 04:55:05PM +0200, Herve Codina wrote:
> > > > Hi Greg,
> > > >
> > > > On Tue, 15 Apr 2025 16:06:43 +0200
> > > > Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > > On Wed, Mar 19, 2025 at 10:52:29PM +0100, Andrea della Porta wrote:
> > > > > > The RaspberryPi RP1 is a PCI multi function device containing
> > > > > > peripherals ranging from Ethernet to USB controller, I2C, SPI
> > > > > > and others.
> > > > >
> > > > > So shouldn't this be using the auxbus code?  That's designed to "split
> > > > > up" PCI devices such that you can share them this way.
> > > > >
> > > > > Or did that get rejected somewhere previously?
> > > > >
> > > >
> > > > It doesn't use auxbus probably for the exact same reason that the
> > > > one given for the LAN966x PCI device driver [0] and [1].
> > > >
> > > > Avoid all boiler plate needed with auxbus whereas drivers already exist
> > > > as platform drivers. Internal devices are handled by those platform drivers.
> > > > Those devi just need to be described as platform devices and device-tree is
> > > > fully relevant for that description.
> > > >
> > > > [0] https://lore.kernel.org/all/CAL_Jsq+1r3SSaXupdNAcXO-4rcV-_3_hwh0XJaBsB9fuX5nBCQ@mail.gmail.com/
> > > > [1] https://lore.kernel.org/all/Y9kuxrL3XaCG+blk@kroah.com/
> > >
> > > I really hate creating platform devices below a PCI device, so I'll keep
> > > complaining about this every time people try to do it.
> >
> > I agree with you, but as Herve has already pointed out this would mean incurring
> > in significant work to adapt drivers for all the peripherals (there are quite a
> > few), while with this approach they would be left untouched.
>
> We have no problem with reworking existing drivers, especially if they
> will be doing the correct thing.  Don't let that be an excuse, it
> doesn't work with me, sorry :)

Let me resurrect of_platform_bus so we can stop repeating the same
conversation... MMIO based devices using DT (and ACPI) are platform
devices. There is no other answer in the kernel today.

Rob