The IRQ module aggregates interrupts from various sources. The interrupt sources are queue-based interrupts, user interrupts and error interrupts.
Queue-based interrupts and user interrupts are allowed on PFs and VFs, but error interrupts are allowed only on PFs. If the SR-IOV is not enabled, each PF has the choice of MSI-X or Legacy Interrupts. With SR-IOV enabled, only MSI-X interrupts are supported across all functions.
MSI-X interrupt is enabled by default. Host system (Root Complex) will enable one or all of the interrupt types supported in hardware. If MSI-X is enabled, it takes precedence.
Up to eight interrupts per function are available. To allow many queues on a given function and each to have interrupts, the QDMA Subsystem for PCIe offers a novel way of aggregating interrupts from multiple queues to a single interrupt vector. In this way, all 2048 queues could in principle be mapped to a single interrupt vector. QDMA offers 256 interrupt aggregation rings that can be flexibly allocated among the 256 available functions.