GIC Software Requirements Specification (SWE.1)
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1 Overview
1.1 Purpose and Role of Module
1.1.1 Module Overview
The Generic Interrupt Controller (GIC) driver is a critical component in ARM-based SoCs, managing interrupts from peripherals to CPU cores. This document specifies the software requirements for the GICv3 and ITS (Interrupt Translation Service) driver, targeting Linux Kernel 6.12. The module ensures that hardware interrupts are correctly routed, prioritized, and handled by the operating system.
1.1.2 Internal and External Factors of Module
| Category | Factors |
|---|---|
| Internal Factors | • Interrupt Handling Logic: Mechanisms to acknowledge, mask, and EOI interrupts. • Register State Machine: Managing GICD/GICR/ITS register states. • Data Structures: gic_chip_data, its_node, bitmap allocators. |
| External Factors | • CPU Cores: Interface with CPU for exception handling. • Peripherals: Devices generating SPIs, PPIs, and MSIs. • Power Management Subsystem: System suspend/resume signals. • Firmware: ACPI tables or Device Tree providing topology info. |
1.2 Hardware Diagram
1.3 Scope of Module
This Software Requirements Specification covers the initialization, configuration, and runtime management of the GICv3 and ITS hardware blocks. It includes:
- Detection of GIC hardware via ACPI/DT.
- Resource allocation for LPIs and MSIs.
- Power management state saving/restoring.
- SMP affinity management.
1.4 Software Context Diagram
2 Feature & Specification
2.1 Feature list
| No | Feature | Details | Remarks |
|---|---|---|---|
| 1 | Initialization | Probing GICv3/ITS hardware and initializing base addresses. | Boot time |
| 2 | Interrupt Routing | Routing SPIs, PPIs, and LPIs to target CPUs. | Runtime |
| 3 | ITS Support | Managing MSI-to-LPI translation for PCI/Platform devices. | Runtime |
| 4 | Power Management | Suspend and Resume support for GIC context. | System Sleep |
2.2 Specification
| No | Item | Specification | Remarks |
|---|---|---|---|
| 1 | Architecture | ARM Generic Interrupt Controller Architecture Specification GICv3/v4 | ARM IHI 0069 |
| 2 | Kernel Version | Linux Kernel 6.12 LTS | |
| 3 | Interface | Linux irq_chip and irq_domain APIs |
3 Requirements
3.1 Functional Requirements
3.1.1 Initialization (REQ-GIC-INIT)
| Attribute | Description |
|---|---|
| Feature | Initialization |
| Quality Attribute | Reliability |
| Input/Stimulus | System Boot, ACPI MADT / Device Tree |
| Output/Response | GICD/GICR mapped, Interrupts enabled, success log in dmesg. |
| Pass/Fail Condition | Driver loads without error; /proc/interrupts shows GIC controller. |
| Verification Method | Unit Test / Integration Test |
| Verification Environment | QEMU / EVB Target |
Detailed Requirements:
- REQ-GIC-INIT-01: The driver SHALL detect the GIC version from the ACPI MADT table or Device Tree compatible string
arm,gic-v3. - REQ-GIC-INIT-02: The driver SHALL map the Distributor (GICD) base address.
- REQ-GIC-INIT-03: The driver SHALL discover and map Redistributors (GICR) for all online CPUs.
3.1.2 Interrupt Routing (REQ-GIC-ROUTE)
| Attribute | Description |
|---|---|
| Feature | Interrupt Routing |
| Quality Attribute | Functionality |
| Input/Stimulus | request_irq(), irq_set_affinity() calls |
| Output/Response | Interrupt delivered to correct CPU core. |
| Pass/Fail Condition | Interrupt counts increment on expected CPU in /proc/interrupts. |
| Verification Method | System Test |
| Verification Environment | EVB Target |
Detailed Requirements:
- REQ-GIC-ROUTE-01: The driver SHALL support routing of Shared Peripheral Interrupts (SPIs) to any online CPU.
- REQ-GIC-ROUTE-02: The driver SHALL support setting the affinity of an interrupt via
irq_set_affinity. - REQ-GIC-ROUTE-03: The driver SHALL route Private Peripheral Interrupts (PPIs) to the specific requesting CPU.
3.1.3 ITS Support (REQ-GIC-ITS)
| Attribute | Description |
|---|---|
| Feature | ITS Support |
| Quality Attribute | Functionality |
| Input/Stimulus | PCI Device Enumeration (MSI Request) |
| Output/Response | LPI allocated, Translation Table updated. |
| Pass/Fail Condition | MSI interrupts function correctly for PCIe devices. |
| Verification Method | Integration Test |
| Verification Environment | EVB Target |
Detailed Requirements:
- REQ-GIC-ITS-01: The driver SHALL detect ITS nodes described in firmware.
- REQ-GIC-ITS-02: The driver SHALL allocate command queues for each ITS.
- REQ-GIC-ITS-03: The driver SHALL manage the translation table to map DeviceID+EventID to LPIs.
3.1.4 Power Management (REQ-GIC-PM)
| Attribute | Description |
|---|---|
| Feature | Power Management |
| Quality Attribute | Reliability |
| Input/Stimulus | pm_suspend command |
| Output/Response | GIC state saved to RAM; System enters sleep. |
| Pass/Fail Condition | System resumes and interrupts function immediately. |
| Verification Method | System Test |
| Verification Environment | EVB Target |
Detailed Requirements:
- REQ-GIC-PM-01: The driver SHALL save the state of GICD and GICR registers upon system suspend.
- REQ-GIC-PM-02: The driver SHALL restore the state of GICD and GICR registers upon system resume.
3.2 Non-Functional Requirements
3.2.1 Quality Requirements
| Attribute | Description |
|---|---|
| Feature | N/A |
| Quality Attribute | Performance (Latency) |
| Input/Stimulus | High-frequency interrupt generation |
| Output/Response | Interrupt service routine execution. |
| Pass/Fail Condition | Latency does not exceed 10 microseconds for LPIs. |
| Verification Method | Performance Measurement |
| Verification Environment | Real-time Kernel Setup |
Detailed Requirements:
- REQ-GIC-NF-01: The driver initialization MUST complete before secondary CPUs are brought up.
- REQ-GIC-NF-02: The interrupt latency introduced by the driver MUST NOT exceed 10 microseconds for LPIs.
3.2.2 Constraints
| Attribute | Description |
|---|---|
| Feature | N/A |
| Constraint | Interface Compliance |
| Description | The driver MUST register with the Linux IRQ subsystem using standard APIs (irq_domain). |
Detailed Requirements:
- REQ-GIC-IF-01: The driver MUST register with the Linux IRQ subsystem using
irq_domain_add_*.
4 Annex
4.1 Annex A. Domain Model
4.2 Annex B. Quality Scenario
Scenario: ITS Interrupt Translation & Latency
4.3 Annex C. Quality Scenario Analysis
Analysis of the above scenarios.
5 Terms and Abbreviations
| Term | Description |
|---|---|
| GIC | Generic Interrupt Controller |
| ITS | Interrupt Translation Service |
| SPI | Shared Peripheral Interrupt |
| PPI | Private Peripheral Interrupt |
| LPI | Locality-specific Peripheral Interrupt |
| MSI | Message Signaled Interrupt |
| ACPI | Advanced Configuration and Power Interface |
| DT | Device Tree |
6 References
| Document Name | Version |
|---|---|
| ARM GICv3 Architecture Specification | IHI 0069H |
| Linux Kernel Source Code | 6.12 |
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