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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 |
+---------+

3.3. Advanced 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, PCH-MSI interrupts go to AVECINTC, and then go to CPUINTC directly, while all other devices interrupts go to PCH-PIC/PCH-LPC and gathered by EIOINTC, and then go to CPUINTC directly:

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

3.4. ACPI-related definitions

CPUINTC:

ACPI_MADT_TYPE_CORE_PIC;
struct acpi_madt_core_pic;
enum acpi_madt_core_pic_version;

LIOINTC:

ACPI_MADT_TYPE_LIO_PIC;
struct acpi_madt_lio_pic;
enum acpi_madt_lio_pic_version;

EIOINTC:

ACPI_MADT_TYPE_EIO_PIC;
struct acpi_madt_eio_pic;
enum acpi_madt_eio_pic_version;

HTVECINTC:

ACPI_MADT_TYPE_HT_PIC;
struct acpi_madt_ht_pic;
enum acpi_madt_ht_pic_version;

PCH-PIC:

ACPI_MADT_TYPE_BIO_PIC;
struct acpi_madt_bio_pic;
enum acpi_madt_bio_pic_version;

PCH-MSI:

ACPI_MADT_TYPE_MSI_PIC;
struct acpi_madt_msi_pic;
enum acpi_madt_msi_pic_version;

PCH-LPC:

ACPI_MADT_TYPE_LPC_PIC;
struct acpi_madt_lpc_pic;
enum acpi_madt_lpc_pic_version;

3.5. References

Documentation of Loongson-3A5000:

https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-3A5000-usermanual-1.02-CN.pdf (in Chinese)

https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-3A5000-usermanual-1.02-EN.pdf (in English)

Documentation of Loongson’s LS7A chipset:

https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-7A1000-usermanual-2.00-CN.pdf (in Chinese)

https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-7A1000-usermanual-2.00-EN.pdf (in English)

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”.