PCI/MSI: Move pci_msi_enabled() to api.c

To disentangle the maze in msi.c, all exported device-driver MSI APIs are
now to be grouped in one file, api.c.

Move pci_msi_enabled() and make its kernel-doc comprehensive.
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20221111122015.271447896@linutronix.de

drivers/pci/msi/api.c

@@ -307,3 +307,15 @@ void pci_free_irq_vectors(struct pci_dev *dev)
 	pci_disable_msi(dev);
 }
 EXPORT_SYMBOL(pci_free_irq_vectors);
+
+/**
+ * pci_msi_enabled() - Are MSI(-X) interrupts enabled system-wide?
+ *
+ * Return: true if MSI has not been globally disabled through ACPI FADT,
+ * PCI bridge quirks, or the "pci=nomsi" kernel command-line option.
+ */
+int pci_msi_enabled(void)
+{
+	return pci_msi_enable;
+}
+EXPORT_SYMBOL(pci_msi_enabled);

drivers/pci/msi/msi.c

@@ -13,7 +13,7 @@
 #include "../pci.h"
 #include "msi.h"
 
-static int pci_msi_enable = 1;
+int pci_msi_enable = 1;
 int pci_msi_ignore_mask;
 
 void pci_msi_update_mask(struct msi_desc *desc, u32 clear, u32 set)
@@ -864,15 +864,3 @@ void pci_no_msi(void)
 {
 	pci_msi_enable = 0;
 }
-
-/**
- * pci_msi_enabled - is MSI enabled?
- *
- * Returns true if MSI has not been disabled by the command-line option
- * pci=nomsi.
- **/
-int pci_msi_enabled(void)
-{
-	return pci_msi_enable;
-}
-EXPORT_SYMBOL(pci_msi_enabled);

drivers/pci/msi/msi.h

@@ -84,6 +84,9 @@ static inline __attribute_const__ u32 msi_multi_mask(struct msi_desc *desc)
 	return (1 << (1 << desc->pci.msi_attrib.multi_cap)) - 1;
 }
 
+/* Subsystem variables */
+extern int pci_msi_enable;
+
 /* MSI internal functions invoked from the public APIs */
 void pci_msi_shutdown(struct pci_dev *dev);
 void pci_msix_shutdown(struct pci_dev *dev);