The chip-level hardware descriptor structure irq_chip contains all the direct chip relevant functions, which can be utilized by the irq flow implementations.
irq_mask_ack() - Optional, recommended for performance
irq_eoi() - Optional, required for EOI flow handlers
irq_retrigger() - Optional
irq_set_type() - Optional
irq_set_wake() - Optional
These primitives are strictly intended to mean what they say: ack means ACK, masking means masking of an IRQ line, etc. It is up to the flow handler(s) to use these basic units of low-level functionality.