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本文转自 周贺贺，baron，代码改变世界ctw，Arm精选， armv8/armv9，trustzone/tee，secureboot，资深安全架构专家，11年手机安全/SOC底层安全开发经验。擅长trustzone/tee安全产品的设计和开发。

1、gic的版本

GIC是一个为Cortex-A和Arm Cortex-R设计的标准的中断控制器

2、GICv3/gicv4的模型图

3、gic中断号的划分

• Shared Peripheral Interrupt (SPI)

• Private Peripheral Interrupt (PPI)

• Software Generated Interrupt (SGI)

• Locality-specific Peripheral Interrupt (LPI)
  
  （使用示例）
  

4、GIC连接方式

5、gic的状态

中断的生命周期:
对于电平触发的中断(level-sensitive interrupts)，一个上升沿输入，将中断变成pending，中断信号线保持高电平直到PE断言该中断信号.
对于边沿触发的中断(edge-sensitive interrupts)，一个上升沿输入，将中断变成pending，中断信号线不会保持高电平.

6、gic框架

• Distributor interface
• Redistributor interface
• CPU interface

Distributor (GICD_*) for SPIs
• Interrupt prioritization and distribution of SPIs
• Enable and disable SPIs
• Set the priority level of each SPI
• Route information for each SPI
• Set each SPI to be level-sensitive or edge-triggered
• Generate message-signaled SPIs
• Control the active and pending state of SPIs
• Determine the programmer’s model that is used in each Security state: affinity routing or legacy

Redistributors (GICR_*)
• Enable and disable SGIs and PPIs
• Set the priority level of SGIs and PPIs
• Set each PPI to be level-sensitive or edge-triggered
• Assign each SGI and PPI to an interrupt group
• Control the state of SGIs and PPIs
• Control the base address for the data structures in memory that support the associated interrupt properties and pending state for LPIs
• Provide power management support for the connected PE

CPU interfaces (ICC_*_ELn)
• Provide general control and configuration to enable interrupt handling
• Acknowledge an interrupt
• Perform a priority drop and deactivation of interrupts
• Set an interrupt priority mask for the PE
• Define the preemption policy for the PE
• Determine the highest priority pending interrupt for the PE

In Arm CoreLink GICv3, the CPU Interface registers are accessed as System registers: ICC_*_ELn.

7、gic Configuring

全局配置
GICD_CTLR.ARE: Enable Affinity routing (ARE bits), 1-使用gicv3 mode，0-使用legacy mode(gicv2 mode). 默认为1
GICD_CTLR.EnableGrp1S
GICD_CTLR.EnableGrp1NS
GICD_CTLR.EnableGrp0

注意在GIC-600 does not support legacy operation

(Redistributor)Settings for each PE
Redistributor中包含了一个GICR_WAKER寄存器，用于记录connected PE的状态是onLine还是offline. 如果让PE变成online，软件则必需这样做：
• Clear GICR_WAKER.ProcessorSleep to 0.
• Poll GICR_WAKER.ChildrenAsleep until it reads 0

如果PE is offline (GICR_WAKER.ProcessorSleep==1)时，来了一个中断target到该PE上，将产一个wake request信号，这个信号连接PE的power controller，该controller将会打开PE。然后PE clear the ProcessorSleep bit

CPU interfaces (ICC_*_ELn)

SRE bit— enable cpu interface
注：有些处理器可能不支持legacy operation，SRE比特位也是固定为1，那么软件就不需要处理该比特了

Set Priority Mask and Binary Point registers
ICC_PMR_EL1、ICC_BPRn_EL1

Set EOI mode （EOI:End of interrupt）
ICC_CTLR_EL1 and ICC_CTLR_EL3

Enable signaling of each interrupt group
ICC_IGRPEN1_EL1 (banked by Security state)
ICC_IGRPEN0_EL1

PE configuration

• Routing controls - SCR_EL3 、 HCR_EL2
• Interrupt masks - PSTATE
• Vector table - VBAR_ELn
  
  
  

interrupt sources configuration

• SPIs are configured through the Distributor, using the GICD_* registers.
• PPIs and SGIs are configured through the individual Redistributors, using the GICR_* registers

对于每一个中断，软件必需配置的：

• Priority: GICD_IPRIORITYn, GICR_IPRIORITYn
• Group: GICD_IGROUPn, GICD_IGRPMODn, GICR_IGROUPn, GICR_IGRPMODn
• Edge-triggered or level-sensitive: GICD_ICFGRn, GICR_ICFGRn
• Enable: GICD_ISENABLERn, GICD_ICENABLER, GICR_ISENABLERn, GICR_ICENABLERn

Setting the target PE for SPIs

• GICD_IROUTERn.Interrupt_Routing_Mode == 0 rounting到制定的PE
• GICD_IROUTERn.Interrupt_Routing_Mode == 1 Distributor硬件会自动选择一个PE，可以是0-n
  A PE can opt out of receiving 1-of-N interrupts. This is controlled by the DPG1S, DPG1NS and DPG0 bits in GICR_CTLR.

Routing a pending interrupt to a PE

• Check that the group associated with the interrupt is enabled
• Check that the interrupt is enabled
• Check the routing controls to decide which PEs can receive the interrupt.
  routing is controlled by GICD_IROUTERn，An SPI can target one specific PE, or any one of the connected PEs
• Check the interrupt priority and priority mask to decide which PEs are suitable to handle the interrupt
  Each PE has a Priority Mask register, ICC_PMR_EL1, in its CPU interface
• Check the running priority to decide which PEs are available to handle the interrup
  Only an interrupt with a higher priority than the running priority can preempt the current interrupt

软件读取中断号

中断优先级

中断结束End of interrupt

• Priority drop - 将中断优先级降到中断产生之前的值
• Deactivation - 将中断从active变成inactive

在gicv3中，drop和deactivation通常是一起打开的。

ICC_CTLR_ELn.EOImode = 1: 通过写ICC_EOIR0_EL1、ICC_EOIR1_EL1让drop and deactivation同时生效
ICC_CTLR_ELn.EOImode = 0: 通过写ICC_EOIR0_EL1、ICC_EOIR1_EL1让drop生效，写ICC_DIR_EL1让deactivation生效，这在虚拟化中会用到.

大多数的软件系统中 EOIMode0，而下hypervisor的系统中 EOIMode1

中断号的状态

产生SGI中断

PE在secure执行时，可以产生secure和non-secure的SGI;
PE在non-secure执行时，也是可以产生secure的SGI，但是取决于GICR_NSACR寄存器的配置，该寄存器只能在secure中读写

比较GICv3和GICv2
在gicv2中，SGI INTIDs对于originating PE和the target PE是banked
在gicv3中，SGI仅仅对target PE是banked

在gicv2中同时收到两个SGI=5中断，两个中断都会被PE处理。
而在gicv3上，由于originating不是banked，所有前一个SGI=5中断将会丢失。PE只能收到一个

Legacy operation

• When ARE==0, affinity routing is disabled (legacy operation)
• When ARE==1, affinity routing is enabled (GICv3 operation)

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