Commit 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI
is disabled") fixed a build error by providing rust helpers when
CONFIG_PCI_MSI=n. However the rust helpers rely on the
pci_alloc_irq_vectors() function is defined, which is not true when
CONFIG_PCI=n. There are multiple ways to fix this, e.g. a possible fix
could be just remove the calling of pci_alloc_irq_vectors() since it's
empty when CONFIG_PCI_MSI=n anyway. However, since PCI irq APIs, such as
pci_alloc_irq_vectors(), are already defined even when CONFIG_PCI=n, the
more reasonable fix is to define pci_alloc_irq_vectors() when
CONFIG_PCI=n and this aligns with the situations of other primitives as
well.

Fixes: 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
I hit a build error without this:

../rust/helpers/pci.c:36:2: error: call to undeclared function 'pci_free_irq_vectors'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   36 |         pci_free_irq_vectors(dev);
      |         ^
../rust/helpers/pci.c:36:2: note: did you mean 'pci_alloc_irq_vectors'?
../include/linux/pci.h:2208:1: note: 'pci_alloc_irq_vectors' declared here
 2208 | pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
      | ^
1 error generated.

when ./tools/testing/kunit/kunit.py run --make_options LLVM=1 --arch arm64 --kconfig_add CONFIG_RUST=y  rust_doctests_kernel

 include/linux/pci.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 864775651c6f..b5cc0c2b9906 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2210,6 +2210,10 @@ pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
 {
 	return -ENOSPC;
 }
+
+static inline void pci_free_irq_vectors(struct pci_dev *dev)
+{
+}
 #endif /* CONFIG_PCI */
 
 /* Include architecture-dependent settings and functions */
-- 
2.51.0

On 12/15/25 3:54 AM, Boqun Feng wrote:
> Commit 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI
> is disabled") fixed a build error by providing rust helpers when
> CONFIG_PCI_MSI=n. However the rust helpers rely on the
> pci_alloc_irq_vectors() function is defined, which is not true when
> CONFIG_PCI=n. There are multiple ways to fix this, e.g. a possible fix
> could be just remove the calling of pci_alloc_irq_vectors() since it's
> empty when CONFIG_PCI_MSI=n anyway. However, since PCI irq APIs, such as
> pci_alloc_irq_vectors(), are already defined even when CONFIG_PCI=n, the
> more reasonable fix is to define pci_alloc_irq_vectors() when
> CONFIG_PCI=n and this aligns with the situations of other primitives as
> well.
> 
> Fixes: 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

Reviewed-by: Danilo Krummrich <dakr@kernel.org>

Bjorn, I assume you will pick this up? Otherwise I can pick it up as well, I
will likely send a -fixes PR for -rc2 anyways.