GIC Software Detailed Design (SWE.3)

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1 Overview

The GIC Software Detailed Design specifies the internal logic, data structures, and algorithms of the GICv3 and ITS driver components. It provides a blueprint for implementation (SWE.4) and ensures that each software unit is verifiable and traceable to the architectural design (SWE.2).

2 Component: GICv3 Core

2.1 Type Definition

| Type Name | Description | | :— | :— | | struct gic_chip_data | Main data structure holding GIC instance state (Distributor base, Redistributor regions). | | struct gic_kvm_info | Structure to pass GIC information to KVM hypervisor. |

2.2 Macro Definition

| Macro Name | Description | | :— | :— | | GICD_CTLR | Offset for Distributor Control Register. | | GICR_WAKER | Offset for Redistributor Waker Register. |

2.3 Global Variables

| Declaration | Type | Description | | :— | :— | :— | | gic_data | struct gic_chip_data | Global instance of the GICv3 driver data. |

2.4 Function Specification

2.4.1 gic_of_init

GUID-358: GICv3 Initialization via Device Tree

• Property: Synchronous, Non-reentrant
• Description: Entry point for GICv3 initialization when booting with Device Tree. Probes hardware, maps registers, and registers the IRQ domain.

Item	Description
Function Scope	Global (init)
Parameters	struct device_node *node, struct device_node *parent
Return	0 on success, negative error code on failure.

3 Component: ITS Driver

3.1 Type Definition

| Type Name | Description | | :— | :— | | struct its_node | Represents a physical ITS hardware block. | | struct its_device | Represents a PCI/Platform device connected to an ITS. |

3.2 Global Variables

| Declaration | Type | Description | | :— | :— | :— | | its_list | struct list_head | List of all probed ITS nodes in the system. |

3.3 Function Specification

3.3.1 its_init

GUID-360: ITS Subsystem Initialization

• Property: Synchronous
• Description: Probes all ITS nodes defined in firmware, allocates command queues, and enables the ITS.

Item	Description
Function Scope	Global (init)
Parameters	None
Return	0 on success.

3.3.2 its_alloc_device

GUID-361: Allocate ITS Device Resources

• Property: Synchronous, Reentrant
• Description: Allocates a unique Device ID and sets up the Device Table entry in the ITS.

Item	Description
Function Scope	Internal
Parameters	struct its_node *its, u32 dev_id, int nvecs
Return	Pointer to struct its_device or NULL.

4 Annex

4.1 Annex A. Evaluation Criteria for Detailed Software Design

The design is evaluated based on HIS metrics:

1. Complexity: Cyclomatic Complexity <= 10.
2. Coupling: Calling Functions <= 5, Called Functions <= 7.

5 Terms and Abbreviations

Terms and Abbreviations	Description
DT	Device Tree
KVM	Kernel-based Virtual Machine

6 References

Documents Name	Version
GIC Software Architectural Design (SWE.2)	1.0
Linux Kernel Source (drivers/irqchip/irq-gic-v3.c)	6.12