[PATCH v2] PCI: rcar-host: Add OF Kconfig dependency to avoid objtool no-cfi warning

[Nathan Chancellor <nathan@kernel.org>]

After commit 894af4a1cde6 ("objtool: Validate kCFI calls"), compile
testing pcie-rcar-host.c with CONFIG_FINEIBT=y and CONFIG_OF=n results
in a no-cfi objtool warning in rcar_pcie_probe():

  $ cat allno.config
  CONFIG_CFI=y
  CONFIG_COMPILE_TEST=y
  CONFIG_CPU_MITIGATIONS=y
  CONFIG_GENERIC_PHY=y
  CONFIG_MITIGATION_RETPOLINE=y
  CONFIG_MODULES=y
  CONFIG_PCI=y
  CONFIG_PCI_MSI=y
  CONFIG_PCIE_RCAR_HOST=y
  CONFIG_X86_KERNEL_IBT=y

  $ make -skj"$(nproc)" ARCH=x86_64 KCONFIG_ALLCONFIG=1 LLVM=1 clean allnoconfig vmlinux
  vmlinux.o: warning: objtool: rcar_pcie_probe+0x191: no-cfi indirect call!

When CONFIG_OF is unset, of_device_get_match_data() returns NULL, so
LLVM knows this indirect call has no valid destination and drops the
kCFI setup before the call, triggering the objtool check that makes sure
all indirect calls have kCFI setup.

This driver depends on OF for probing with non-NULL data for every match
so this call will never be NULL in practice. Add a hard Kconfig
dependency on OF to avoid the warning.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202510092124.O2IX0Jek-lkp@intel.com/
Closes: https://github.com/ClangBuiltLinux/linux/issues/2134
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
Changes in v2:
- Switch from NULL check to avoiding CONFIG_OF=n case altogether (Mani,
  Geert).
- Drop Peter and Kees's reviews, as solution is not the same.
- Link to v1: https://patch.msgid.link/20251013-rcar_pcie_probe-avoid-nocfi-objtool-warning-v1-1-552876b94f04@kernel.org
---
 drivers/pci/controller/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
index 41748d083b93..d8688abc5b27 100644
--- a/drivers/pci/controller/Kconfig
+++ b/drivers/pci/controller/Kconfig
@@ -243,6 +243,7 @@ config PCI_TEGRA
 config PCIE_RCAR_HOST
 	bool "Renesas R-Car PCIe controller (host mode)"
 	depends on ARCH_RENESAS || COMPILE_TEST
+	depends on OF
 	depends on PCI_MSI
 	select IRQ_MSI_LIB
 	help

---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251013-rcar_pcie_probe-avoid-nocfi-objtool-warning-1a975accb6b6

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>