calling one of the irq_domain_add_*() functions (each mapping method
has a different allocator function, more on that later). The function
will return a pointer to the irq_domain on success. The caller must
-provide the allocator function with an irq_domain_ops structure with
-the .map callback populated as a minimum.
+provide the allocator function with an irq_domain_ops structure.
In most cases, the irq_domain will begin empty without any mappings
between hwirq and IRQ numbers. Mappings are added to the irq_domain