linux-kernel - Re: [PATCH v9 1/6] misc: Add support for LAN966x PCI device

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Message-ID: <CAMuHMdWgqEZtd82hSp0iYahtTcTnORFytTm11EiZOjLf8V9tQw@mail.gmail.com>
Date: Fri, 29 Nov 2024 11:29:44 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Herve Codina <herve.codina@...tlin.com>, Michal Kubecek <mkubecek@...e.cz>, 
	Andy Shevchenko <andy.shevchenko@...il.com>, Simon Horman <horms@...nel.org>, Lee Jones <lee@...nel.org>, 
	"derek.kiernan@....com" <derek.kiernan@....com>, "dragan.cvetic@....com" <dragan.cvetic@....com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 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>, 
	UNGLinuxDriver@...rochip.com, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Saravana Kannan <saravanak@...gle.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>, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Netdev <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 v9 1/6] misc: Add support for LAN966x PCI device

Hi Arnd,

On Fri, Nov 29, 2024 at 10:23 AM Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Nov 29, 2024, at 09:44, Geert Uytterhoeven wrote:
> > On Fri, Nov 29, 2024 at 9:25 AM Arnd Bergmann <arnd@...db.de> wrote:
> >> On Fri, Nov 29, 2024, at 09:10, Herve Codina wrote:
> >> I would write in two lines as
> >>
> >>         depends on PCI
> >>         depends on OF_OVERLAY
> >>
> >> since OF_OVERLAY already depends on OF, that can be left out.
> >> The effect is the same as your variant though.
> >
> > What about
> >
> >     depends on OF
> >     select OF_OVERLAY
> >
> > as "OF" is a clear bus dependency, due to the driver providing an OF
> > child bus (cfr. I2C or SPI bus controller drivers depending on I2C or
> > SPI), and OF_OVERLAY is an optional software mechanism?
>
> OF_OVERLAY is currently a user visible option, so I think it's
> intended to be used with 'depends on'. The only other callers
> of this interface are the kunit test modules that just leave
> out the overlay code if that is disabled.

Indeed, there are no real upstream users of OF_OVERLAY left.
Until commit 1760eb547276299a ("drm: rcar-du: Drop leftovers
dependencies from Kconfig"), the rcar-lvds driver selected OF_OVERLAY
to be able to fix up old DTBs.

> If we decide to treat OF_OVERLAY as a library instead, it should
> probably become a silent Kconfig option that gets selected by
> all its users including the unit tests, and then we can remove
> the #ifdef checks there.

Yep.

> Since OF_OVERLAY pulls in OF_DYNAMIC, I would still prefer that
> to be a user choice. Silently enabling OF_OVERLAY definitely has
> a risk of introducing regressions since it changes some of the
> interesting code paths in the core, in particular it enables
> reference counting in of_node_get(), which many drivers get wrong.

Distro kernels will have to enable this anyway, if they want to
support LAN966x...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds