linux-kernel - Re: [PATCH RESEND v11 10/13] um: nommu: a work around for MMU dependency to PCI driver

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Message-ID: <m2zfak7mnd.wl-thehajime@gmail.com>
Date: Wed, 24 Sep 2025 08:51:50 +0900
From: Hajime Tazaki <thehajime@...il.com>
To: johannes@...solutions.net
Cc: geert@...ux-m68k.org,
	linux-um@...ts.infradead.org,
	ricarkol@...gle.com,
	Liam.Howlett@...cle.com,
	linux-kernel@...r.kernel.org,
	arnd@...db.de
Subject: Re: [PATCH RESEND v11 10/13] um: nommu: a work around for MMU dependency to PCI driver


Hello Geert, Johannes,

On Wed, 24 Sep 2025 02:13:47 +0900,
Johannes Berg wrote:
> 
> On Tue, 2025-09-23 at 17:42 +0200, Geert Uytterhoeven wrote:
> > > 
> > > currently, drivers/pci/Kconfig (CONFIG_PCI) marks as depends on MMU,
> > > so we cannot select it when CONFIG_MMU=n.
> > 
> > That is a fairly recent change, see commit 8fe743b5eba0abfb ("PCI:
> > Add CONFIG_MMU dependency") in v6.16-rc1.  As this is not a "hard"
> > dependency, perhaps it should be reverted, iff you are willing to take
> > care of the casual breakage?
> 
> Why though? UML with PCI can't really be a functional thing, only a
> testing thing, and testing PCI on !MMU when that is actually impossible
> in non-simulation is pointless?

currently nommu UML doesn't come with using PCI except building under
kunit (ARCH=um), but I have in my mind to use it under !MMU
environment, so would be an option in the future.

and this series doesn't include PCI w/ !MMU.

so, I would propose the modification to revert the MMU dependency when
time has come.

btw, what do you mean by "hard" dependency in this context, Geert ? 

-- Hajime