linux-kernel - [PATCH] pci: provide pci_free_irq_vectors() stub when CONFIG

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Message-Id: <20251222034415.1384223-1-buaajxlj@163.com>
Date: Mon, 22 Dec 2025 11:44:15 +0800
From: Liang Jie <buaajxlj@....com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	linux-pci@...r.kernel.org (open list:PCI SUBSYSTEM),
	linux-kernel@...r.kernel.org (open list),
	rust-for-linux@...r.kernel.org (open list:RUST:Keyword:\b(?i:rust)\b),
	llvm@...ts.linux.dev (open list:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b)
Cc: liangjie@...iang.com,
	kernel test robot <lkp@...el.com>
Subject: [PATCH] pci: provide pci_free_irq_vectors() stub when CONFIG_PCI is disabled

From: Liang Jie <liangjie@...iang.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@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512220740.4Kexm4dW-lkp@intel.com/
Signed-off-by: Liang Jie <liangjie@...iang.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