Docs/LoongArch: Add advanced extended IRQ model description

Introduce the advanced extended interrupt controllers (AVECINTC). This
feature will allow each core to have 256 independent interrupt vectors
and MSI interrupts can be independently routed to any vector on any CPU.

The whole topology of irqchips in LoongArch machines looks like this if
AVECINTC is supported:

  +-----+     +-----------------------+     +-------+
  | IPI | --> |        CPUINTC        | <-- | Timer |
  +-----+     +-----------------------+     +-------+
               ^          ^          ^
               |          |          |
        +---------+ +----------+ +---------+     +-------+
        | EIOINTC | | AVECINTC | | LIOINTC | <-- | UARTs |
        +---------+ +----------+ +---------+     +-------+
             ^            ^
             |            |
        +---------+  +---------+
        | PCH-PIC |  | PCH-MSI |
        +---------+  +---------+
          ^     ^           ^
          |     |           |
  +---------+ +---------+ +---------+
  | Devices | | PCH-LPC | | Devices |
  +---------+ +---------+ +---------+
                   ^
                   |
              +---------+
              | Devices |
              +---------+
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>

Documentation/arch/loongarch/irq-chip-model.rst

@@ -85,6 +85,38 @@ to CPUINTC directly::
     | Devices |
     +---------+
 
+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 |
+             +---------+
+
 ACPI-related definitions
 ========================
 

Documentation/translations/zh_CN/arch/loongarch/irq-chip-model.rst

@@ -87,6 +87,38 @@ PCH-LPC/PCH-MSI，然后被EIOINTC统一收集，再直接到达CPUINTC::
     | Devices |
     +---------+
 
+高级扩展IRQ模型
+===============
+
+在这种模型里面，IPI（Inter-Processor Interrupt）和CPU本地时钟中断直接发送到CPUINTC，
+CPU串口（UARTs）中断发送到LIOINTC，PCH-MSI中断发送到AVECINTC，而后通过AVECINTC直接
+送达CPUINTC，而其他所有设备的中断则分别发送到所连接的PCH-PIC/PCH-LPC，然后由EIOINTC
+统一收集，再直接到达CPUINTC::
+
+ +-----+     +-----------------------+     +-------+
+ | IPI | --> |        CPUINTC        | <-- | Timer |
+ +-----+     +-----------------------+     +-------+
+              ^          ^          ^
+              |          |          |
+       +---------+ +----------+ +---------+     +-------+
+       | EIOINTC | | AVECINTC | | LIOINTC | <-- | UARTs |
+       +---------+ +----------+ +---------+     +-------+
+            ^            ^
+            |            |
+       +---------+  +---------+
+       | PCH-PIC |  | PCH-MSI |
+       +---------+  +---------+
+         ^     ^           ^
+         |     |           |
+ +---------+ +---------+ +---------+
+ | Devices | | PCH-LPC | | Devices |
+ +---------+ +---------+ +---------+
+                  ^
+                  |
+             +---------+
+             | Devices |
+             +---------+
+
 ACPI相关的定义
 ==============