genirq/msi: Provide msi_domain_ops:: Post_free()

To prepare for removing the exposure of __msi_domain_free_irqs() provide a
post_free() callback in the MSI domain ops which can be used to solve
the problem of the only user of __msi_domain_free_irqs() in arch/powerpc.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20221111122014.063153448@linutronix.de

include/linux/msi.h

@@ -315,6 +315,8 @@ struct msi_domain_info;
  *			function.
  * @domain_free_irqs:	Optional function to override the default free
  *			function.
+ * @msi_post_free:	Optional function which is invoked after freeing
+ *			all interrupts.
  *
  * @get_hwirq, @msi_init and @msi_free are callbacks used by the underlying
  * irqdomain.
@@ -359,6 +361,8 @@ struct msi_domain_ops {
 					     struct device *dev, int nvec);
 	void		(*domain_free_irqs)(struct irq_domain *domain,
 					    struct device *dev);
+	void		(*msi_post_free)(struct irq_domain *domain,
+					 struct device *dev);
 };
 
 /**

kernel/irq/msi.c

@@ -1026,6 +1026,8 @@ void msi_domain_free_irqs_descs_locked(struct irq_domain *domain, struct device
 	lockdep_assert_held(&dev->msi.data->mutex);
 
 	ops->domain_free_irqs(domain, dev);
+	if (ops->msi_post_free)
+		ops->msi_post_free(domain, dev);
 	msi_domain_free_msi_descs(info, dev);
 }