[patch RFC 30/38] PCI/MSI: Allow to disable arch fallbacks

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

If an architecture does not require the MSI setup/teardown fallback
functions, then allow them to be replaced by stub functions which emit a
warning.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: linux-pci@xxxxxxxxxxxxxxx
---
 drivers/pci/Kconfig |    3 +++
 drivers/pci/msi.c   |    3 ++-
 include/linux/msi.h |   31 ++++++++++++++++++++++++++-----
 3 files changed, 31 insertions(+), 6 deletions(-)

--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -56,6 +56,9 @@ config PCI_MSI_IRQ_DOMAIN
        depends on PCI_MSI
        select GENERIC_MSI_IRQ_DOMAIN
 
+config PCI_MSI_DISABLE_ARCH_FALLBACKS
+       bool
+
 config PCI_QUIRKS
        default y
        bool "Enable PCI quirk workarounds" if EXPERT
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -58,8 +58,8 @@ static void pci_msi_teardown_msi_irqs(st
 #define pci_msi_teardown_msi_irqs      arch_teardown_msi_irqs
 #endif
 
+#ifndef CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS
 /* Arch hooks */
-
 int __weak arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc)
 {
        struct msi_controller *chip = dev->bus->msi;
@@ -132,6 +132,7 @@ void __weak arch_teardown_msi_irqs(struc
 {
        return default_teardown_msi_irqs(dev);
 }
+#endif /* !CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS */
 
 static void default_restore_msi_irq(struct pci_dev *dev, int irq)
 {
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -193,17 +193,38 @@ void pci_msi_mask_irq(struct irq_data *d
 void pci_msi_unmask_irq(struct irq_data *data);
 
 /*
- * The arch hooks to setup up msi irqs. Those functions are
- * implemented as weak symbols so that they /can/ be overriden by
- * architecture specific code if needed.
+ * The arch hooks to setup up msi irqs. Default functions are implemented
+ * as weak symbols so that they /can/ be overriden by architecture specific
+ * code if needed.
+ *
+ * They can be replaced by stubs with warnings via
+ * CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS when the architecture fully
+ * utilizes direct irqdomain based setup.
  */
+#ifndef CONFIG_PCI_MSI_DISABLE_ARCH_FALLBACKS
 int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc);
 void arch_teardown_msi_irq(unsigned int irq);
 int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type);
 void arch_teardown_msi_irqs(struct pci_dev *dev);
-void arch_restore_msi_irqs(struct pci_dev *dev);
-
 void default_teardown_msi_irqs(struct pci_dev *dev);
+#else
+static inline int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
+{
+       WARN_ON_ONCE(1);
+       return -ENODEV;
+}
+
+static inline void arch_teardown_msi_irqs(struct pci_dev *dev)
+{
+       WARN_ON_ONCE(1);
+}
+#endif
+
+/*
+ * The restore hooks are still available as they are useful even
+ * for fully irq domain based setups. Courtesy to XEN/X86.
+ */
+void arch_restore_msi_irqs(struct pci_dev *dev);
 void default_restore_msi_irqs(struct pci_dev *dev);
 
 struct msi_controller {