对于一个系统来说，管理中断描述符也是一个值得考量的问题，如果中断个数有限，并且分布连续，则使用一个数组
较为简单，而如果中断分散，则采用动态分配较为可观，内核在配置CONFIG_SPARSE_IRQ时，采用动态分配中断
描述符。在非配置情形下则使用一个固定数组跟踪所有的中断描述符，即中断描述符表，数组形式如下：
struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
[0 ... NR_IRQS-1] = {
.handle_irq = handle_bad_irq,
.depth = 1,
.lock = __RAW_SPIN_LOCK_UNLOCKED(irq_desc->lock),
}
};
显然这里通过NR_IRQS定义了数组长度。
这种情形下，所有的中断描述符管理非常简单。
1. IRQ号到中断描述符
struct irq_desc *irq_to_desc(unsigned int irq)
{
return (irq < NR_IRQS) ? irq_desc + irq : NULL;
}
EXPORT_SYMBOL(irq_to_desc);
2. 分配连续多个中断描述符
static inline int alloc_descs(unsigned int start, unsigned int cnt, int node,
const struct cpumask *affinity,
struct module *owner)
{
u32 i;
for (i = 0; i < cnt; i++) {
struct irq_desc *desc = irq_to_desc(start + i);
desc->owner = owner;
}
return start;
}
3. 初始化函数
int __init early_irq_init(void)
{
int count, i, node = first_online_node;
struct irq_desc *desc;
init_irq_default_affinity();
printk(KERN_INFO "NR_IRQS:%d\n", NR_IRQS);
desc = irq_desc;
count = ARRAY_SIZE(irq_desc);
for (i = 0; i < count; i++) {
desc[i].kstat_irqs = alloc_percpu(unsigned int);
alloc_masks(&desc[i], GFP_KERNEL, node);
raw_spin_lock_init(&desc[i].lock);
lockdep_set_class(&desc[i].lock, &irq_desc_lock_class);
desc_set_defaults(i, &desc[i], node, NULL, NULL);
}
return arch_early_irq_init();
}
4. 释放IRQ描述符
static void free_desc(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
unsigned long flags;
raw_spin_lock_irqsave(&desc->lock, flags);
desc_set_defaults(irq, desc, irq_desc_get_node(desc), NULL, NULL);
raw_spin_unlock_irqrestore(&desc->lock, flags);
}
