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: <m28qib8g1r.wl-thehajime@gmail.com>
Date: Fri, 19 Sep 2025 09:03:12 +0900
From: Hajime Tazaki <thehajime@...il.com>
To: johannes@...solutions.net
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 Thu, 18 Sep 2025 17:30:22 +0900,
Johannes Berg wrote:
> 
> On Thu, 2025-09-18 at 16:39 +0900, Hajime Tazaki wrote:
> > The commit 8fe743b5eba0 ("PCI: Add CONFIG_MMU dependency") restricts the
> > PCI base driver to depend on MMU.  While nommu UML _can_ implement PCI
> > drivers over PCI devices (e.g., virtio-pci), the current nommu UML
> > doesn't implement it.
> > 
> > But without PCI drivers kunit complains as config for kunit
> > (arch_uml.config) defines the dependency to PCI drivers.
> > 
> > This commit fixes the issue of this compile failures when building PCI
> > drivers with nommu UML.  In particular, the fix is to undefine the
> > constant PCI_IOBASE to be able to bypass pci_unmap_iospace() call.
> 
> 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).

so I'll drop this patch in the next version.

thanks,
-- Hajime