Linux Irq domain

Posted 2022-10-23 Loopers

本节学习下什么是irq domain, 以及irq domain的作用。可以参考内核文档IRQ-domain.txt

为什么引入IRQ-Domain

当早期的系统只存在一个interrupt-controller的时候，而且中断数目也不多的时候，一个很简单的做法就是一个中断号对应到interrupt-contoller的一个号，可以说是简单的线性映射

而当一个系统中有多个interrupt-controller的时候，而且中断号也逐渐增加。linux内核为了应对此问题，引入了IRQ-domain的概念

 

irq-domain的引入相当于一个中断控制器就是一个irq-domain。就是一个中断区域。这样一来所有的irq-contoller会出现级联的布局。

利用树状的结构可以充分的利用irq数目，而且每一个irq-domain区域可以自己去管理自己interrupt的特性

IRQ-Domain的作用

咋们通过/proc/interrupt的值来看下irq-domain的作用

 从这图上可以看出，这些中断只直接连接到root-interrupt-controller的，也就是直接连接到GICv3的中断控制器上的。而Hwirq-num就是dts中配置的irq号

而第一列就是对应的softirq-num，也就是request_irq时传入的irq

 

中断控制器级联的情况图

 

hwirq到softirq的映射

当开机之后，内核会自动将dts全部解析，然后会进行填充，对于中断使用如下函数进行解析dts，然后map

unsigned int irq_of_parse_and_map(struct device_node *dev, int index)

    struct of_phandle_args oirq;
 
    if (of_irq_parse_one(dev, index, &oirq))
        return 0;
 
    return irq_create_of_mapping(&oirq);

of_irq_parse_one会将dts中的中断信息进行解析，然后通过irq_create_of_mapping函数进行hwirq到softirq的map

• 首先dts中配置的中断号都是hwirq
• 刚开机hwirq没有对应的softirq的，所以第一次开机需要进行hwirq和softirq之间建立map

int irq_domain_alloc_descs(int virq, unsigned int cnt, irq_hw_number_t hwirq,
               int node, const struct cpumask *affinity)

    unsigned int hint;
 
    if (virq >= 0) 
        virq = __irq_alloc_descs(virq, virq, cnt, node, THIS_MODULE,
                     affinity);
     else 
        hint = hwirq % nr_irqs;
        if (hint == 0)
            hint++;
        virq = __irq_alloc_descs(-1, hint, cnt, node, THIS_MODULE,
                     affinity);
        if (virq <= 0 && hint > 1) 
            virq = __irq_alloc_descs(-1, 1, cnt, node, THIS_MODULE,
                         affinity);
        
    
 
    return virq;

通过上述的函数分配virq，也就是softirq
 

static struct irq_data *irq_domain_insert_irq_data(struct irq_domain *domain,
                           struct irq_data *child)

    struct irq_data *irq_data;
 
    irq_data = kzalloc_node(sizeof(*irq_data), GFP_KERNEL,
                irq_data_get_node(child));
    if (irq_data) 
        child->parent_data = irq_data;
        irq_data->irq = child->irq;
        irq_data->common = child->common;
        irq_data->domain = domain;
    
 
    return irq_data;

分配一个Irq_data结构，然后将virq设置到irq_data结构中

static void irq_domain_set_mapping(struct irq_domain *domain,
                   irq_hw_number_t hwirq,
                   struct irq_data *irq_data)

    if (hwirq < domain->revmap_size) 
        domain->linear_revmap[hwirq] = irq_data->irq;
     else 
        mutex_lock(&domain->revmap_tree_mutex);
        radix_tree_insert(&domain->revmap_tree, hwirq, irq_data);
        mutex_unlock(&domain->revmap_tree_mutex);
    

将hwirq和irq_data→irq建立映射。这里有两种映射方式一种是线性映射，一种是树形映射

 

irq和irq_desc的关系

在分配一个softirq的时候，其实最终也会分配一个irq_desc结构的

这里有两种管理方式，一种是通过线性固定开机固定分配好了的，一种是动态分配的

static struct irq_desc *alloc_desc(int irq, int node, unsigned int flags,
                   const struct cpumask *affinity,
                   struct module *owner)

    struct irq_desc *desc;
 
    desc = kzalloc_node(sizeof(*desc), GFP_KERNEL, node);
    if (!desc)
        return NULL;
    /* allocate based on nr_cpu_ids */
    desc->kstat_irqs = alloc_percpu(unsigned int);
    if (!desc->kstat_irqs)
        goto err_desc;
 
    if (alloc_masks(desc, node))
        goto err_kstat;
 
    raw_spin_lock_init(&desc->lock);
    lockdep_set_class(&desc->lock, &irq_desc_lock_class);
    mutex_init(&desc->request_mutex);
    init_rcu_head(&desc->rcu);
 
    desc_set_defaults(irq, desc, node, affinity, owner);
    irqd_set(&desc->irq_data, flags);
    kobject_init(&desc->kobj, &irq_kobj_type);
 
    return desc;
 
err_kstat:
    free_percpu(desc->kstat_irqs);
err_desc:
    kfree(desc);
    return NULL;

开机已经分配好了的，用于irq比较少

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),
    
;

通过irq_to_desc函数来获取desc通过irq的值,两种方式

struct irq_desc *irq_to_desc(unsigned int irq)

    return radix_tree_lookup(&irq_desc_tree, irq);

 
 
struct irq_desc *irq_to_desc(unsigned int irq)

    return (irq < NR_IRQS) ? irq_desc + irq : NULL;

申请中断

通过request_irq函数来设置中断的回调函数，最终会设置到Irqaction中去

int request_threaded_irq(unsigned int irq, irq_handler_t handler,
             irq_handler_t thread_fn, unsigned long irqflags,
             const char *devname, void *dev_id)

    struct irqaction *action;
    struct irq_desc *desc;
 
 
 
 
    action->handler = handler;                   //设置中断回调函数
    action->thread_fn = thread_fn;               //如果中断是线程化，则需要设置此回调
    action->flags = irqflags;
    action->name = devname;
    action->dev_id = dev_id; 
 
 

 

处理中断

irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags)

    irqreturn_t retval = IRQ_NONE;
    unsigned int irq = desc->irq_data.irq;
    struct irqaction *action;
 
    record_irq_time(desc);
 
    for_each_action_of_desc(desc, action) 
        irqreturn_t res;
 
        trace_irq_handler_entry(irq, action);
        res = action->handler(irq, action->dev_id);           //处理中断
        trace_irq_handler_exit(irq, action, res);
 
        if (WARN_ONCE(!irqs_disabled(),"irq %u handler %pF enabled interrupts\\n",
                  irq, action->handler))
            local_irq_disable();
 
        switch (res) 
        case IRQ_WAKE_THREAD:
            /*
             * Catch drivers which return WAKE_THREAD but
             * did not set up a thread function
             */
            if (unlikely(!action->thread_fn)) 
                warn_no_thread(irq, action);
                break;
            
 
            __irq_wake_thread(desc, action);
 
            /* Fall through to add to randomness */
        case IRQ_HANDLED:
            *flags |= action->flags;
            break;
 
        default:
            break;
        
 
        retval |= res;
    
 
    return retval;

• 处理中断，action->handler(irq, action->dev_id);
• 如果是中断线程的话，唤醒线程 __irq_wake_thread(desc, action);