From: Liang Jie <liangjie@lixiang.com>

When building with CONFIG_PCI=n, clang reports:

  In file included from rust/helpers/helpers.c:40:
  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]
          pci_free_irq_vectors(dev);
          ^
  rust/helpers/pci.c:36:2: note: did you mean 'pci_alloc_irq_vectors'?
  include/linux/pci.h:2161:1: note: 'pci_alloc_irq_vectors' declared here
  pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
  ^
  1 error generated.

The root cause is that include/linux/pci.h provides inline stubs for
pci_alloc_irq_vectors() in the CONFIG_PCI=n fallback, but does not provide
any declaration for pci_free_irq_vectors(). As a result, callers that invoke
pci_free_irq_vectors() under CONFIG_PCI=n (e.g. Rust PCI helpers) hit an
implicit function declaration error with clang.

Fix this by adding a no-op pci_free_irq_vectors() stub to the CONFIG_PCI=n
fallback section of include/linux/pci.h, keeping the alloc/free API pair
consistent and avoiding implicit declaration build failures.

Fixes: 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512220740.4Kexm4dW-lkp@intel.com/
Signed-off-by: Liang Jie <liangjie@lixiang.com>
---
 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 */
-- 
2.25.1

On 22.12.25 04:44, Liang Jie wrote:
> From: Liang Jie <liangjie@lixiang.com>
> 
> When building with CONFIG_PCI=n, clang reports:
> 
>   In file included from rust/helpers/helpers.c:40:
>   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]
>           pci_free_irq_vectors(dev);
>           ^
>   rust/helpers/pci.c:36:2: note: did you mean 'pci_alloc_irq_vectors'?
>   include/linux/pci.h:2161:1: note: 'pci_alloc_irq_vectors' declared here
>   pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
>   ^
>   1 error generated.
> 
> The root cause is that include/linux/pci.h provides inline stubs for
> pci_alloc_irq_vectors() in the CONFIG_PCI=n fallback, but does not provide
> any declaration for pci_free_irq_vectors(). As a result, callers that invoke
> pci_free_irq_vectors() under CONFIG_PCI=n (e.g. Rust PCI helpers) hit an
> implicit function declaration error with clang.
> 
> Fix this by adding a no-op pci_free_irq_vectors() stub to the CONFIG_PCI=n
> fallback section of include/linux/pci.h, keeping the alloc/free API pair
> consistent and avoiding implicit declaration build failures.
> 
> Fixes: 473b9f331718 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202512220740.4Kexm4dW-lkp@intel.com/
> Signed-off-by: Liang Jie <liangjie@lixiang.com>
> ---
>  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 */

We have this from Boqun already

https://lore.kernel.org/rust-for-linux/20251215025444.65544-1-boqun.feng@gmail.com/

?

Dirk

On 22 Dec 2025 08:02:44 +0100, Dirk Behme wrote:
> On 22.12.25 04:44, Liang Jie wrote:
> > From: Liang Jie <liangjie@lixiang.com>
> > 
> > When building with CONFIG_PCI=n, clang reports:
> > 
> >          ....
> >
> >  /* Include architecture-dependent settings and functions */
> 
> We have this from Boqun already
> 
> https://lore.kernel.org/rust-for-linux/20251215025444.65544-1-boqun.feng@gmail.com/
> 
> ?
> 
> Dirk

Hi Dirk,

Sorry, I missed Boqun's earlier patch:
https://lore.kernel.org/rust-for-linux/20251215025444.65544-1-boqun.feng@gmail.com/

It addresses the same issue. Please ignore my patch.

Thanks,
Liang