3. IRQ chip model (hierarchy) of LoongArch

Currently, LoongArch based processors (e.g. Loongson-3A5000) can only work together with LS7A chipsets. The irq chips in LoongArch computers include CPUINTC (CPU Core Interrupt Controller), LIOINTC (Legacy I/O Interrupt Controller), EIOINTC (Extended I/O Interrupt Controller), HTVECINTC (Hyper-Transport Vector Interrupt Controller), PCH-PIC (Main Interrupt Controller in LS7A chipset), PCH-LPC (LPC Interrupt Controller in LS7A chipset) and PCH-MSI (MSI Interrupt Controller).

CPUINTC is a per-core controller (in CPU), LIOINTC/EIOINTC/HTVECINTC are per-package controllers (in CPU), while PCH-PIC/PCH-LPC/PCH-MSI are controllers out of CPU (i.e., in chipsets). These controllers (in other words, irqchips) are linked in a hierarchy, and there are two models of hierarchy (legacy model and extended model).

3.1. Legacy IRQ model

In this model, IPI (Inter-Processor Interrupt) and CPU Local Timer interrupt go to CPUINTC directly, CPU UARTS interrupts go to LIOINTC, while all other devices interrupts go to PCH-PIC/PCH-LPC/PCH-MSI and gathered by HTVECINTC, and then go to LIOINTC, and then CPUINTC:

+-----+     +---------+     +-------+
| IPI | --> | CPUINTC | <-- | Timer |
+-----+     +---------+     +-------+
                 ^
                 |
            +---------+     +-------+
            | LIOINTC | <-- | UARTs |
            +---------+     +-------+
                 ^
                 |
           +-----------+
           | HTVECINTC |
           +-----------+
            ^         ^
            |         |
      +---------+ +---------+
      | PCH-PIC | | PCH-MSI |
      +---------+ +---------+
        ^     ^           ^
        |     |           |
+---------+ +---------+ +---------+
| PCH-LPC | | Devices | | Devices |
+---------+ +---------+ +---------+
     ^
     |
+---------+
| Devices |
+---------+

3.2. Extended IRQ model

In this model, IPI (Inter-Processor Interrupt) and CPU Local Timer interrupt go to CPUINTC directly, CPU UARTS interrupts go to LIOINTC, while all other devices interrupts go to PCH-PIC/PCH-LPC/PCH-MSI and gathered by EIOINTC, and then go to to CPUINTC directly:

      +-----+     +---------+     +-------+
      | IPI | --> | CPUINTC | <-- | Timer |
      +-----+     +---------+     +-------+
                   ^       ^
                   |       |
            +---------+ +---------+     +-------+
            | EIOINTC | | LIOINTC | <-- | UARTs |
            +---------+ +---------+     +-------+
             ^       ^
             |       |
      +---------+ +---------+
      | PCH-PIC | | PCH-MSI |
      +---------+ +---------+
        ^     ^           ^
        |     |           |
+---------+ +---------+ +---------+
| PCH-LPC | | Devices | | Devices |
+---------+ +---------+ +---------+
     ^
     |
+---------+
| Devices |
+---------+

3.4. References

Documentation of Loongson-3A5000:

Documentation of Loongson's LS7A chipset:

Note

  • CPUINTC is CSR.ECFG/CSR.ESTAT and its interrupt controller described in Section 7.4 of "LoongArch Reference Manual, Vol 1";

  • LIOINTC is "Legacy I/OInterrupts" described in Section 11.1 of "Loongson 3A5000 Processor Reference Manual";

  • EIOINTC is "Extended I/O Interrupts" described in Section 11.2 of "Loongson 3A5000 Processor Reference Manual";

  • HTVECINTC is "HyperTransport Interrupts" described in Section 14.3 of "Loongson 3A5000 Processor Reference Manual";

  • PCH-PIC/PCH-MSI is "Interrupt Controller" described in Section 5 of "Loongson 7A1000 Bridge User Manual";

  • PCH-LPC is "LPC Interrupts" described in Section 24.3 of "Loongson 7A1000 Bridge User Manual".