genirq/irqdomain: Provide IRQ_DOMAIN_FLAG_MSI_PARENT

The new PCI/IMS (Interrupt Message Store) functionality is allowing
hardware vendors to provide implementation specific storage for the MSI
messages. This can be device memory and also host/guest memory, e.g. in
queue memory which is shared with the hardware.

This requires device specific MSI interrupt domains, which cannot be
achieved by expanding the existing PCI/MSI interrupt domain concept which is
a global interrupt domain shared by all PCI devices on a particular (IOMMU)
segment:

                                         |--- device 1
     [Vector]---[Remapping]---[PCI/MSI]--|...
                                         |--- device N

This works because the PCI/MSI[-X] space is uniform, but falls apart with
PCI/IMS which is implementation defined and must be available along with
PCI/MSI[-X] on the same device.

To support PCI/MSI[-X] plus PCI/IMS on the same device it is required to
rework the PCI/MSI interrupt domain hierarchy concept in the following way:

                              |--- [PCI/MSI] device 1
     [Vector]---[Remapping]---|...
                              |--- [PCI/MSI] device N

That allows in the next step to create multiple interrupt domains per device:


                              |--- [PCI/MSI] device 1
                              |--- [PCI/IMS] device 1
     [Vector]---[Remapping]---|...
                              |--- [PCI/MSI] device N
                              |--- [PCI/IMS] device N

So the domain which previously created the global PCI/MSI domain must now
act as parent domain for the per device domains.

The hierarchy depth is the same as before, but the PCI/MSI domains are then
device specific and not longer global.

Provide IRQ_DOMAIN_FLAG_MSI_PARENT, which allows to identify these parent
domains, along with helpers to query it.
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/20221124230313.690038274@linutronix.de

include/linux/irqdomain.h

@@ -189,6 +189,9 @@ enum {
 	/* Irq domain doesn't translate anything */
 	IRQ_DOMAIN_FLAG_NO_MAP		= (1 << 6),
 
+	/* Irq domain is a MSI parent domain */
+	IRQ_DOMAIN_FLAG_MSI_PARENT	= (1 << 8),
+
 	/*
 	 * Flags starting from IRQ_DOMAIN_FLAG_NONCORE are reserved
 	 * for implementation specific purposes and ignored by the
@@ -551,6 +554,11 @@ static inline bool irq_domain_is_msi_remap(struct irq_domain *domain)
 
 extern bool irq_domain_hierarchical_is_msi_remap(struct irq_domain *domain);
 
+static inline bool irq_domain_is_msi_parent(struct irq_domain *domain)
+{
+	return domain->flags & IRQ_DOMAIN_FLAG_MSI_PARENT;
+}
+
 #else	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
 static inline int irq_domain_alloc_irqs(struct irq_domain *domain,
 			unsigned int nr_irqs, int node, void *arg)
@@ -596,6 +604,12 @@ irq_domain_hierarchical_is_msi_remap(struct irq_domain *domain)
 {
 	return false;
 }
+
+static inline bool irq_domain_is_msi_parent(struct irq_domain *domain)
+{
+	return false;
+}
+
 #endif	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
 
 #else /* CONFIG_IRQ_DOMAIN */