acpi/irq: Implement helper to create hierachical domains

ACPI permits arbitrary producer->consumer interrupt links to be
described in AML, which means a topology such as the following
is perfectly legal:

  Device (EXIU) {
    Name (_HID, "SCX0008")
    Name (_UID, Zero)
    Name (_CRS, ResourceTemplate () {
      ...
    })
  }

  Device (GPIO) {
    Name (_HID, "SCX0007")
    Name (_UID, Zero)
    Name (_CRS, ResourceTemplate () {
      Memory32Fixed (ReadWrite, SYNQUACER_GPIO_BASE, SYNQUACER_GPIO_SIZE)
      Interrupt (ResourceConsumer, Edge, ActiveHigh, ExclusiveAndWake, 0, "\\_SB.EXIU") {
        7,
      }
    })
    ...
  }

The EXIU in this example is the external interrupt unit as can be found
on Socionext SynQuacer based platforms, which converts a block of 32 SPIs
from arbitrary polarity/trigger into level-high, with a separate set
of config/mask/unmask/clear controls.

The existing DT based driver in drivers/irqchip/irq-sni-exiu.c models
this as a hierarchical domain stacked on top of the GIC's irqdomain.
Since the GIC is modeled as a DT node as well, obtaining a reference
to this irqdomain is easily done by going through the parent link.

On ACPI systems, however, the GIC is not modeled as an object in the
namespace, and so device objects cannot refer to it directly. So in
order to obtain the irqdomain reference when driving the EXIU in ACPI
mode, we need a helper that implicitly grabs the default domain as the
parent of the hierarchy for interrupts allocated out of the global GSI
pool.
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/acpi/irq.c

@@ -295,3 +295,29 @@ void __init acpi_set_irq_model(enum acpi_irq_model_id model,
 	acpi_irq_model = model;
 	acpi_gsi_domain_id = fwnode;
 }
+
+/**
+ * acpi_irq_create_hierarchy - Create a hierarchical IRQ domain with the default
+ *                             GSI domain as its parent.
+ * @flags:      Irq domain flags associated with the domain
+ * @size:       Size of the domain.
+ * @fwnode:     Optional fwnode of the interrupt controller
+ * @ops:        Pointer to the interrupt domain callbacks
+ * @host_data:  Controller private data pointer
+ */
+struct irq_domain *acpi_irq_create_hierarchy(unsigned int flags,
+					     unsigned int size,
+					     struct fwnode_handle *fwnode,
+					     const struct irq_domain_ops *ops,
+					     void *host_data)
+{
+	struct irq_domain *d = irq_find_matching_fwnode(acpi_gsi_domain_id,
+							DOMAIN_BUS_ANY);
+
+	if (!d)
+		return NULL;
+
+	return irq_domain_create_hierarchy(d, flags, size, fwnode, ops,
+					   host_data);
+}
+EXPORT_SYMBOL_GPL(acpi_irq_create_hierarchy);

include/linux/acpi.h

@@ -23,6 +23,7 @@
 
 #include <linux/errno.h>
 #include <linux/ioport.h>	/* for struct resource */
+#include <linux/irqdomain.h>
 #include <linux/resource_ext.h>
 #include <linux/device.h>
 #include <linux/property.h>
@@ -327,6 +328,12 @@ int acpi_isa_irq_to_gsi (unsigned isa_irq, u32 *gsi);
 void acpi_set_irq_model(enum acpi_irq_model_id model,
 			struct fwnode_handle *fwnode);
 
+struct irq_domain *acpi_irq_create_hierarchy(unsigned int flags,
+					     unsigned int size,
+					     struct fwnode_handle *fwnode,
+					     const struct irq_domain_ops *ops,
+					     void *host_data);
+
 #ifdef CONFIG_X86_IO_APIC
 extern int acpi_get_override_irq(u32 gsi, int *trigger, int *polarity);
 #else