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: <6b1abe384237c8129e8043ecdfdad77758d2fd2f.camel@sipsolutions.net>
Date: Fri, 19 Sep 2025 09:24:07 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Hajime Tazaki <thehajime@...il.com>
Cc: linux-um@...ts.infradead.org, ricarkol@...gle.com,
 Liam.Howlett@...cle.com, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v11 10/13] um: nommu: a work around for MMU
 dependency to PCI driver

On Fri, 2025-09-19 at 09:03 +0900, Hajime Tazaki wrote:
> > This doesn't make a lot of sense to me. Why would we even want to build
> > PCI on NOMMU-UML if PCI in general is dependent on MMU now?
> > 
> > It's not like ARCH=um with PCI and NOMMU has any value even for testing
> > if such a configuration cannot exist in reality?
> 
> totally understand your point.
> 
> now I see that we don't have to have this work around by using
> --kconfig_add option to kunit.py.
> 
> # like --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=n (in addition to
>   --kconfig_add CONFIG_MMU=n).

That's not what I mean. I think it should be made impossible to build
the broken code.

The problem is probably UML_PCI_OVER_VIRTIO selecting UML_PCI selecting
various PCI code, but nothing depends on PCI in the first place. Which
it should, then?

johannes