[PATCH] genirq/msi: add stubs for get_cached_msi_msg/pci_write_msi_msg

[Arnd Bergmann]

A bug fix to the MSIx handling in vfio added references to functions
that may not be defined if MSI is disabled in the kernel, resulting in
this link error:

drivers/built-in.o: In function `vfio_msi_set_vector_signal':
:(.text+0x450808): undefined reference to `get_cached_msi_msg'
:(.text+0x45080c): undefined reference to `write_msi_msg'

As suggested by Alex Williamson, this adds stub implementations for
get_cached_msi_msg() and pci_write_msi_msg().

In case this bugfix gets backported, please note that the #ifdef
has changed over time, originally both functions were implemented
in drivers/pci/msi.c and controlled by CONFIG_PCI_MSI, while nowadays
get_cached_msi_msg() is part of the generic MSI support and can be
used without PCI.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: b8f02af096b1 ("vfio/pci: Restore MSIx message prior to enabling")
Link: https://lkml.org/lkml/2014/10/13/124
---
I had a workaround for this hidden in my randconfig tree but have
now stumbled over it again, sorry for not following up a couple of years
earlier.
---
 include/linux/msi.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/msi.h b/include/linux/msi.h
index 0db320b7bb15..a83b84ff70e5 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -17,7 +17,13 @@ struct msi_desc;
 struct pci_dev;
 struct platform_msi_priv_data;
 void __get_cached_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
+#ifdef CONFIG_GENERIC_MSI_IRQ
 void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg);
+#else
+static inline void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
+{
+}
+#endif
 
 typedef void (*irq_write_msi_msg_t)(struct msi_desc *desc,
 				    struct msi_msg *msg);
@@ -116,11 +122,15 @@ struct msi_desc {
 
 struct pci_dev *msi_desc_to_pci_dev(struct msi_desc *desc);
 void *msi_desc_to_pci_sysdata(struct msi_desc *desc);
+void pci_write_msi_msg(unsigned int irq, struct msi_msg *msg);
 #else /* CONFIG_PCI_MSI */
 static inline void *msi_desc_to_pci_sysdata(struct msi_desc *desc)
 {
 	return NULL;
 }
+static inline void pci_write_msi_msg(unsigned int irq, struct msi_msg *msg)
+{
+}
 #endif /* CONFIG_PCI_MSI */
 
 struct msi_desc *alloc_msi_entry(struct device *dev, int nvec,
@@ -128,7 +138,6 @@ struct msi_desc *alloc_msi_entry(struct device *dev, int nvec,
 void free_msi_entry(struct msi_desc *entry);
 void __pci_read_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
 void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
-void pci_write_msi_msg(unsigned int irq, struct msi_msg *msg);
 
 u32 __pci_msix_desc_mask_irq(struct msi_desc *desc, u32 flag);
 u32 __pci_msi_desc_mask_irq(struct msi_desc *desc, u32 mask, u32 flag);
-- 
2.9.0