Re: [PATCH] PCI: Provide pci_free_irq_vectors() for CONFIG_PCI=n

[Drew Fustini <fustini@kernel.org>]

On Mon, Dec 15, 2025 at 11:54:44AM +0900, 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>
> ---
> 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
> 

Reviewed-by: Drew Fustini <fustini@kernel.org>

Thanks for the fix. I ran into this when building next-20251217 for a
machine without PCIe and was happy to find this on lore.

Drew