linux-kernel - Re: [PATCH v3 6/7] mfd: Add support for LAN966x PCI device

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Message-ID: <CAL_Jsq+1r3SSaXupdNAcXO-4rcV-_3_hwh0XJaBsB9fuX5nBCQ@mail.gmail.com>
Date: Thu, 11 Jul 2024 14:33:26 -0600
From: Rob Herring <robh@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Herve Codina <herve.codina@...tlin.com>, Lee Jones <lee@...nel.org>, 
	Andy Shevchenko <andy.shevchenko@...il.com>, Simon Horman <horms@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	UNGLinuxDriver@...rochip.com, Saravana Kannan <saravanak@...gle.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Philipp Zabel <p.zabel@...gutronix.de>, 
	Lars Povlsen <lars.povlsen@...rochip.com>, Steen Hegelund <Steen.Hegelund@...rochip.com>, 
	Daniel Machon <daniel.machon@...rochip.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Horatiu Vultur <horatiu.vultur@...rochip.com>, Andrew Lunn <andrew@...n.ch>, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	netdev@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, 
	Allan Nielsen <allan.nielsen@...rochip.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 6/7] mfd: Add support for LAN966x PCI device

On Thu, Jul 11, 2024 at 1:08 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Jul 11, 2024 at 06:44:38PM +0200, Herve Codina wrote:
> > Hi Lee,
> >
> > On Thu, 11 Jul 2024 16:29:52 +0100
> > Lee Jones <lee@...nel.org> wrote:
> >
> > > On Thu, 27 Jun 2024, Herve Codina wrote:
> > >
> > > > Add a PCI driver that handles the LAN966x PCI device using a device-tree
> > > > overlay. This overlay is applied to the PCI device DT node and allows to
> > > > describe components that are present in the device.
> > > >
> > > > The memory from the device-tree is remapped to the BAR memory thanks to
> > > > "ranges" properties computed at runtime by the PCI core during the PCI
> > > > enumeration.
> > > >
> > > > The PCI device itself acts as an interrupt controller and is used as the
> > > > parent of the internal LAN966x interrupt controller to route the
> > > > interrupts to the assigned PCI INTx interrupt.
> > >
> > > Not entirely sure why this is in MFD.
> >
> > This PCI driver purpose is to instanciate many other drivers using a DT
> > overlay. I think MFD is the right subsystem.

It is a Multi-function Device, but it doesn't appear to use any of the
MFD subsystem. So maybe drivers/soc/? Another dumping ground, but it
is a driver for an SoC exposed as a PCI device.

> Please use the aux bus for that, that is what is was specifically
> designed for, and what it is being used for today.

We discussed this already[1]. Different usecase, but needs the same thing.

Like I said before, the bus and device used for DT MMIO devices is
like it or not platform bus/device.

In this case, all the child devices are already supported as platform
devices. There would be zero benefit to add all the boilerplate to
make their drivers both platform and aux bus drivers. Plus there is
zero DT support in aux bus.

Rob

[1] https://lore.kernel.org/all/Y9kuxrL3XaCG+blk@kroah.com/