JJJ--linux irq

以imx6u为例：
有两处调用了irq_domain_add_linear向系统注册irq domain 线性映射。没有no_map和Radix_Tree_map这两种方式（irq_domain_add_nomap 和 irq_domain_add_tree）

调用栈2处分别为：

1、

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.15 #1
Hardware name: Freescale i.MX6 Ultralite (Device Tree)
[<80015ed4>] (unwind_backtrace) from [<80012794>] (show_stack+0x10/0x14)
[<80012794>] (show_stack) from [<806f2218>] (dump_stack+0x80/0xc8)
[<806f2218>] (dump_stack) from [<809dc3bc>] (gic_init_bases+0xa4/0x280)
[<809dc3bc>] (gic_init_bases) from [<809dc648>] (gic_of_init+0xb0/0x108)
[<809dc648>] (gic_of_init) from [<809e76ec>] (of_irq_init+0x158/0x278)
[<809e76ec>] (of_irq_init) from [<809a4328>] (init_IRQ+0x28/0x84)
[<809a4328>] (init_IRQ) from [<809a1ac4>] (start_kernel+0x210/0x3a0)
[<809a1ac4>] (start_kernel) from [<8000807c>] (0x8000807c)

2、

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.15 #1
Hardware name: Freescale i.MX6 Ultralite (Device Tree)
[<80015ed4>] (unwind_backtrace) from [<80012794>] (show_stack+0x10/0x14)
[<80012794>] (show_stack) from [<806f2218>] (dump_stack+0x80/0xc8)
[<806f2218>] (dump_stack) from [<80075498>] (irq_domain_add_hierarchy+0x38/0xc8)
[<80075498>] (irq_domain_add_hierarchy) from [<809aec20>] (imx_gpc_init+0xa0/0x2a0)
[<809aec20>] (imx_gpc_init) from [<809e76ec>] (of_irq_init+0x158/0x278)
[<809e76ec>] (of_irq_init) from [<809a4328>] (init_IRQ+0x28/0x84)
[<809a4328>] (init_IRQ) from [<809a1ac4>] (start_kernel+0x210/0x3a0)
[<809a1ac4>] (start_kernel) from [<8000807c>] (0x8000807c)

由start_kernel找到init_IRQ（arch/arm/kernel/irq.c），到irqchip_init（drivers/irqchip/irqchip.c），到of_irq_init(__irqchip_of_table) drivers/of/irq.c

/**
 * of_irq_init - Scan and init matching interrupt controllers in DT
 * @matches: 0 terminated array of nodes to match and init function to call
 *
 * This function scans the device tree for matching interrupt controller nodes,
 * and calls their initialization functions in order with parents first.
 */
void __init of_irq_init(const struct of_device_id *matches)
{
    struct device_node *np, *parent = NULL;
    struct intc_desc *desc, *temp_desc;
    struct list_head intc_desc_list, intc_parent_list;

    INIT_LIST_HEAD(&intc_desc_list);
    INIT_LIST_HEAD(&intc_parent_list);

    for_each_matching_node(np, matches) {
    	// 这个属性位于imx6ull.dtsi中的interrupt-controller@00a01000节点内部
        if (!of_find_property(np, "interrupt-controller", NULL) ||
                !of_device_is_available(np))   //节点的status为ok或者okey，或者没有status属性就返回true
            continue;
		/*
         * Here, we allocate and populate an intc_desc with the node
         * pointer, interrupt-parent device_node etc.
         */
        desc = kzalloc(sizeof(*desc), GFP_KERNEL);
        if (WARN_ON(!desc))
            goto err;

        desc->dev = np;
        desc->interrupt_parent = of_irq_find_parent(np);
        if (desc->interrupt_parent == np)
            desc->interrupt_parent = NULL;
        list_add_tail(&desc->list, &intc_desc_list);
    }

    /*
     * The root irq controller is the one without an interrupt-parent.
     * That one goes first, followed by the controllers that reference it,
     * followed by the ones that reference the 2nd level controllers, etc.
     */
    while (!list_empty(&intc_desc_list)) {
        /*
         * Process all controllers with the current 'parent'.
         * First pass will be looking for NULL as the parent.
         * The assumption is that NULL parent means a root controller.
         */
        list_for_each_entry_safe(desc, temp_desc, &intc_desc_list, list) {
            const struct of_device_id *match;
            int ret;
        	if (desc->interrupt_parent != parent)
                continue;

            list_del(&desc->list);
            match = of_match_node(matches, desc->dev);
            if (WARN(!match->data,
                "of_irq_init: no init function for %s\n",
                match->compatible)) {
                kfree(desc);
                continue;
            }

            pr_debug("of_irq_init: init %s @ %p, parent %p\n",
                 match->compatible,
                 desc->dev, desc->interrupt_parent);
            irq_init_cb = (of_irq_init_cb_t)match->data;
            ret = irq_init_cb(desc->dev, desc->interrupt_parent);
            if (ret) {
                kfree(desc);
                continue;
            }

            /*
             * This one is now set up; add it to the parent list so
             * its children can get processed in a subsequent pass.
             */
            list_add_tail(&desc->list, &intc_parent_list);
        }

        /* Get the next pending parent that might have children */
        desc = list_first_entry_or_null(&intc_parent_list,
                        typeof(*desc), list);
        if (!desc) {
        	pr_err("of_irq_init: children remain, but no parents\n");
            break;
        }
        list_del(&desc->list);
        parent = desc->dev;
        kfree(desc);
    }

    list_for_each_entry_safe(desc, temp_desc, &intc_parent_list, list) {
        list_del(&desc->list);
        kfree(desc);
    }
err:
    list_for_each_entry_safe(desc, temp_desc, &intc_desc_list, list) {
        list_del(&desc->list);
        kfree(desc);
    }
}
                                         

下面是2个struct of_device_id类型的条目，是irq控制器初始化相关：
1、

// drivers/irqchip/irq-gic.c
IRQCHIP_DECLARE(cortex_a7_gic, "arm,cortex-a7-gic", gic_of_init);

// drivers/irqchip/irqchip.h
#define IRQCHIP_DECLARE(name, compat, fn) OF_DECLARE_2(irqchip, name, compat, fn)
OF_DECLARE_2(irqchip, cortex_a7_gic, "arm,cortex-a7-gic", gic_of_init);

//include/linux/of.h
#define OF_DECLARE_2(table, name, compat, fn) \
	_OF_DECLARE(table, name, compat, fn, of_init_fn_2)

_OF_DECLARE(irqchip, cortex_a7_gic, "arm,cortex-a7-gic", gic_of_init, of_init_fn_2)

// include/linux/of.h
#define _OF_DECLARE(table, name, compat, fn, fn_type)           \
    static const struct of_device_id __of_table_##name      \
        __used __section(__##table##_of_table)          \
         = { .compatible = compat,              \
             .data = (fn == (fn_type)NULL) ? fn : fn  }

static const struct of_device_id __of_table_cortex_a7_gic
		__used __section(__irqchip_of_table)
		 = {.compatible = "arm,cortex-a7-gic", 
			.data = (gic_of_init == (of_init_fn_2)NULL?gic_of_init:gic_of_init   }

通过"arm,cortex-a7-gic"匹配，将match->data赋值给init_urq_cb，即gic_of_init，并执行

2、

// arch/arm/mach-imx/gpc.c
OF_DECLARE_2(irqchip, imx_gpc, "fsl,imx6q-gpc", imx_gpc_init);
...
static const struct of_device_id __of_table_imx_gpc
		__used __section(__irqchip_of_table)
		= {.compatible = "fsl,imx6q-gpc",
			.data = (imx_gpc_init == (of_init_fn_2)NULL?imx_gpc_init:imx_gpc_init)}

找出这两个compat对应的设备节点：

// imx6ull.dtsi
...
intc: interrupt-controller@00a01000 {
        compatible = "arm,cortex-a7-gic";
        #interrupt-cells = <3>;
        interrupt-controller;
        reg = <0x00a01000 0x1000>,
              <0x00a02000 0x100>;
    };
...
 gpc: gpc@020dc000 {
                compatible = "fsl,imx6ul-gpc", "fsl,imx6q-gpc";
                reg = <0x020dc000 0x4000>;
                interrupt-controller;
                #interrupt-cells = <3>;
                interrupts = <GIC_SPI 89 IRQ_TYPE_LEVEL_HIGH>;
                interrupt-parent = <&intc>;
                fsl,mf-mix-wakeup-irq = <0xfc00000 0x7d00 0x0 0x1400640>;
            };
...

先看 gic_of_init：在drivers/irqchip/irq-gic.c
gic_of_init