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+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================
+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).
+
+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 |
+ +---------+
+
+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 |
+ +---------+
+
+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;
+
+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".