[PATCH] kunit: Enable PCI on UML without triggering WARN()

[PATCH] kunit: Enable PCI on UML without triggering WARN()

[Thomas Weißschuh]

Various KUnit tests require PCI infrastructure to work.
All normal platforms enable PCI by default, but UML does not.
Enabling PCI from .kunitconfig files is problematic as it would not be
portable. So in commit 6fc3a8636a7b ("kunit: tool: Enable virtio/PCI by default on UML")
PCI was enabled by way of CONFIG_UML_PCI_OVER_VIRTIO=y.
However CONFIG_UML_PCI_OVER_VIRTIO requires additional configuration of
CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID or will otherwise trigger a WARN() in
virtio_pcidev_init(). However there is no one correct value for
UML_PCI_OVER_VIRTIO_DEVICE_ID which could be used by default.

This warning is confusing when debugging test failures.

On the other hand, the functionality of CONFIG_UML_PCI_OVER_VIRTIO is not
used at all, given that it is completely non-functional as indicated by
the WARN() in question. Instead it is only used as a way to enable
CONFIG_UML_PCI which itself is not directly configurable.

Instead of going through CONFIG_UML_PCI_OVER_VIRTIO, introduce a custom
configuration option which enables CONFIG_UML_PCI without triggering
warnings or building dead code.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 lib/kunit/Kconfig                           | 7 +++++++
 tools/testing/kunit/configs/arch_uml.config | 5 ++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index a97897edd9642f3e5df7fdd9dee26ee5cf00d6a4..c8ca155521b2455a221ddbec3f6fc55662c83475 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -93,4 +93,11 @@ config KUNIT_AUTORUN_ENABLED
 	  In most cases this should be left as Y. Only if additional opt-in
 	  behavior is needed should this be set to N.
 
+config KUNIT_UML_PCI
+	bool "KUnit UML PCI Support"
+	depends on UML
+	select UML_PCI
+	help
+	  Enables the PCI subsystem on UML for use by KUnit tests.
+
 endif # KUNIT
diff --git a/tools/testing/kunit/configs/arch_uml.config b/tools/testing/kunit/configs/arch_uml.config
index 54ad8972681a2cc724e6122b19407188910b9025..28edf816aa70e6f408d9486efff8898df79ee090 100644
--- a/tools/testing/kunit/configs/arch_uml.config
+++ b/tools/testing/kunit/configs/arch_uml.config
@@ -1,8 +1,7 @@
 # Config options which are added to UML builds by default
 
-# Enable virtio/pci, as a lot of tests require it.
-CONFIG_VIRTIO_UML=y
-CONFIG_UML_PCI_OVER_VIRTIO=y
+# Enable pci, as a lot of tests require it.
+CONFIG_KUNIT_UML_PCI=y
 
 # Enable FORTIFY_SOURCE for wider checking.
 CONFIG_FORTIFY_SOURCE=y

---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250626-kunit-uml-pci-a2b687553746

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@linutronix.de>

Re: [PATCH] kunit: Enable PCI on UML without triggering WARN()

[Johannes Berg]

On Fri, 2025-06-27 at 17:21 +0200, Thomas Weißschuh wrote:
> Various KUnit tests require PCI infrastructure to work.
> All normal platforms enable PCI by default, but UML does not.
> Enabling PCI from .kunitconfig files is problematic as it would not be
> portable. So in commit 6fc3a8636a7b ("kunit: tool: Enable virtio/PCI by default on UML")
> PCI was enabled by way of CONFIG_UML_PCI_OVER_VIRTIO=y.
> However CONFIG_UML_PCI_OVER_VIRTIO requires additional configuration of
> CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID or will otherwise trigger a WARN() in
> virtio_pcidev_init(). However there is no one correct value for
> UML_PCI_OVER_VIRTIO_DEVICE_ID which could be used by default.
> 
> This warning is confusing when debugging test failures.
> 
> On the other hand, the functionality of CONFIG_UML_PCI_OVER_VIRTIO is not
> used at all, given that it is completely non-functional as indicated by
> the WARN() in question. Instead it is only used as a way to enable
> CONFIG_UML_PCI which itself is not directly configurable.
> 
> Instead of going through CONFIG_UML_PCI_OVER_VIRTIO, introduce a custom
> configuration option which enables CONFIG_UML_PCI without triggering
> warnings or building dead code.

Alright, so looked like Thomas wanted this to not be merged via the UML
tree, which does make sense, so I've dropped it.

For the kunit tree then you can add:

Reviewed-by: Johannes Berg <johannes@sipsolutions.net>

johannes