genirq/msi: Create msi_api.h

Create a API header for MSI specific functions which are relevant to device
drivers.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124230313.632679220@linutronix.de

include/linux/msi.h

@@ -13,11 +13,14 @@
  *
  * Regular device drivers have no business with any of these functions and
  * especially storing MSI descriptor pointers in random code is considered
- * abuse. The only function which is relevant for drivers is msi_get_virq().
+ * abuse.
+ *
+ * Device driver relevant functions are available in <linux/msi_api.h>
  */
 
 #include <linux/irqdomain_defs.h>
 #include <linux/cpumask.h>
+#include <linux/msi_api.h>
 #include <linux/xarray.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
@@ -188,7 +191,6 @@ struct msi_device_data {
 
 int msi_setup_device_data(struct device *dev);
 
-unsigned int msi_get_virq(struct device *dev, unsigned int index);
 void msi_lock_descs(struct device *dev);
 void msi_unlock_descs(struct device *dev);
 

include/linux/msi_api.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LINUX_MSI_API_H
+#define LINUX_MSI_API_H
+
+/*
+ * APIs which are relevant for device driver code for allocating and
+ * freeing MSI interrupts and querying the associations between
+ * hardware/software MSI indices and the Linux interrupt number.
+ */
+
+struct device;
+
+unsigned int msi_get_virq(struct device *dev, unsigned int index);
+
+#endif