Linux中断子系统：级联中断控制器驱动

Linux中断子系统

Linux中断子系统是个很大的话题，如下面的思维导图所示，包含硬件、驱动、中断上半部、中断下半部等等。本文着眼于中断控制器（PIC），特别是级联中断控制器驱动部分，对驱动的设计和调试要点进行分析总结。

 

级联中断控制器驱动

中断控制器的核心对象是irq_chip，其提供了很多接口，一般情况下不需要全部实现。下面是几个类似的接口的差别介绍：

1. irq_enable：在中断注册或使能时调用，一般在使能中断前需要清除中断状态。
2. irq_disable：在中断注销或关闭时调用，一般在关闭中断前不清除中断状态。
3. irq_mask_ack：在进入中断处理函数前调用，一般在屏蔽中断前需要清除中断源信号。
4. irq_unmask：在退出中断处理函数后调用，一般在去屏蔽中断前不清除清除中断源信号。

级联中断控制器的初始化流程

中断控制器的级联如上图所示。级联中断控制器的初始化流程分为2部分：根中断控制器的初始化和子中断控制器的初始化。

根中断控制器相关部分

1. 根据irq获取根PIC的irt；
2. 将irt/irq的映射关系配置到根PIC的IRT表寄存器；
3. 初始化根PIC的irq_chip接口对象；
4. 调用irq_set_chip_and_handler设置根PIC irq的irq_chip及其handler；
5. 调用irq_set_chip_data设置根PIC irq_chip接口调用时的环境对象；

子中断控制器相关部分

1. 初始化子PIC的irq_chip接口对象；
2. 映射子PIC io mem空间，以便后续访问其寄存器；
3. 获取PIC的irq domain的irq基值，并调用irq_domain_add_xxx获取子PIC的中断域空间；
4. 调用irq_set_chip_and_handler设置子PIC irq的irq_chip及其handler；
5. 调用irq_set_chip_data设置子PIC irq_chip接口调用时的环境对象；
6. 获取根PIC的irq；
7. 调用irq_set_chained_handler设置根PIC irq handler；
8. 调用irq_set_handler_data设置根PIC irq handler调用时的环境对象；

级联中断控制器的中断处理流程

首先，CPU只能感知到root PIC的中断，当root PIC的中断触发后，进入root irq handler，在handler中找到触发中断的sub irq，并调用其handler进行中断处理。换句话说，root irq的handler是root PIC的中断路由功能的软件扩展。

找到sub irq的方法依赖sub PIC具体硬件实现，以GPIO中断控制器的root irq handler为例，其方法如下：

1. 调用chained_irq_enter，mask_ack root irq；
2. 获取gpio 中断pin脚使能情况；
3. 读取gpio interrupt status寄存器，判断此gpio 中断使能pin脚是否触发了中断；
4. 通过irq_find_mapping获取此gpio pin对应的irq#；
5. 通过generic_handle_irq调用 sub irq handler来进行gpio中断处理；
6. 调用chained_irq_exit，unmask root irq。

中断控制器驱动调试要点

1. 根据中断控制器特点，仔细设计irq_chip的接口。那么哪些需要实现，哪些又不需要是需要仔细考虑；
2. root irq的handler要用chained_irq_enter/chained_irq_exit进行保护；
3. 理顺中断触发时序。比如设备、子PIC的中断状态、中断源信号等中断标记清除顺序，以此来决定在哪些irq_chip接口中清除中断标记；
4. 一般来说，对于任何中断设备，在使能中断前需要清除中断状态，避免垃圾中断干扰。

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/**  * struct irq_chip - hardware interrupt chip descriptor  *  * @name:       name for /proc/interrupts  * @irq_startup:    start up the interrupt (defaults to ->enable if NULL)  * @irq_shutdown:   shut down the interrupt (defaults to ->disable if NULL)  * @irq_enable:     enable the interrupt (defaults to chip->unmask if NULL)  * @irq_disable:    disable the interrupt  * @irq_ack:        start of a new interrupt  * @irq_mask:       mask an interrupt source  * @irq_mask_ack:   ack and mask an interrupt source  * @irq_unmask:     unmask an interrupt source  * @irq_eoi:        end of interrupt  * @irq_set_affinity:   set the CPU affinity on SMP machines  * @irq_retrigger:  resend an IRQ to the CPU  * @irq_set_type:   set the flow type (IRQ_TYPE_LEVEL/etc.) of an IRQ  * @irq_set_wake:   enable/disable power-management wake-on of an IRQ  * @irq_bus_lock:   function to lock access to slow bus (i2c) chips  * @irq_bus_sync_unlock:function to sync and unlock slow bus (i2c) chips  * @irq_cpu_online: configure an interrupt source for a secondary CPU  * @irq_cpu_offline:    un-configure an interrupt source for a secondary CPU  * @irq_suspend:    function called from core code on suspend once per chip  * @irq_resume:     function called from core code on resume once per chip  * @irq_pm_shutdown:    function called from core code on shutdown once per chip  * @irq_print_chip: optional to print special chip info in show_interrupts  * @flags:      chip specific flags  */ struct irq_chip {     const char  *name;     unsigned int    (*irq_startup)(struct irq_data *data);     void        (*irq_shutdown)(struct irq_data *data);     void        (*irq_enable)(struct irq_data *data);     void        (*irq_disable)(struct irq_data *data);       void        (*irq_ack)(struct irq_data *data);     void        (*irq_mask)(struct irq_data *data);     void        (*irq_mask_ack)(struct irq_data *data);     void        (*irq_unmask)(struct irq_data *data);     void        (*irq_eoi)(struct irq_data *data);       int     (*irq_set_affinity)(struct irq_data *data, const struct cpumask *dest, bool force);     int     (*irq_retrigger)(struct irq_data *data);     int     (*irq_set_type)(struct irq_data *data, unsigned int flow_type);     int     (*irq_set_wake)(struct irq_data *data, unsigned int on);       void        (*irq_bus_lock)(struct irq_data *data);     void        (*irq_bus_sync_unlock)(struct irq_data *data);       void        (*irq_cpu_online)(struct irq_data *data);     void        (*irq_cpu_offline)(struct irq_data *data);       void        (*irq_suspend)(struct irq_data *data);     void        (*irq_resume)(struct irq_data *data);     void        (*irq_pm_shutdown)(struct irq_data *data);       void        (*irq_print_chip)(struct irq_data *data, struct seq_file *p);       unsigned long   flags; };   /**  * struct irq_data - per irq and irq chip data passed down to chip functions  * @irq:        interrupt number  * @hwirq:      hardware interrupt number, local to the interrupt domain  * @node:       node index useful for balancing  * @state_use_accessors: status information for irq chip functions.  *          Use accessor functions to deal with it  * @chip:       low level interrupt hardware access  * @domain:     Interrupt translation domain; responsible for mapping  *          between hwirq number and linux irq number.  * @handler_data:   per-IRQ data for the irq_chip methods  * @chip_data:      platform-specific per-chip private data for the chip  *          methods, to allow shared chip implementations  * @msi_desc:       MSI descriptor  * @affinity:       IRQ affinity on SMP  *  * The fields here need to overlay the ones in irq_desc until we  * cleaned up the direct references and switched everything over to  * irq_data.  */ struct irq_data {     unsigned int        irq;     unsigned long       hwirq;     unsigned int        node;     unsigned int        state_use_accessors;     struct irq_chip     *chip;     struct irq_domain   *domain;     void            *handler_data;     void            *chip_data;     struct msi_desc     *msi_desc;     cpumask_var_t       affinity; };   /**  * struct irq_desc - interrupt descriptor  * @irq_data:       per irq and chip data passed down to chip functions  * @kstat_irqs:     irq stats per cpu  * @handle_irq:     highlevel irq-events handler  * @preflow_handler:    handler called before the flow handler (currently used by sparc)  * @action:     the irq action chain  * @status:     status information  * @core_internal_state__do_not_mess_with_it: core internal status information  * @depth:      disable-depth, for nested irq_disable() calls  * @wake_depth:     enable depth, for multiple irq_set_irq_wake() callers  * @irq_count:      stats field to detect stalled irqs  * @last_unhandled: aging timer for unhandled count  * @irqs_unhandled: stats field for spurious unhandled interrupts  * @lock:       locking for SMP  * @affinity_hint:  hint to user space for preferred irq affinity  * @affinity_notify:    context for notification of affinity changes  * @pending_mask:   pending rebalanced interrupts  * @threads_oneshot:    bitfield to handle shared oneshot threads  * @threads_active: number of irqaction threads currently running  * @wait_for_threads:   wait queue for sync_irq to wait for threaded handlers  * @dir:        /proc/irq/ procfs entry  * @name:       flow handler name for /proc/interrupts output  */ struct irq_desc {     struct irq_data     irq_data;     unsigned int __percpu   *kstat_irqs;     irq_flow_handler_t  handle_irq; #ifdef CONFIG_IRQ_PREFLOW_FASTEOI     irq_preflow_handler_t   preflow_handler; #endif     struct irqaction    *action;    /* IRQ action list */     unsigned int        status_use_accessors;     unsigned int        core_internal_state__do_not_mess_with_it;     unsigned int        depth;      /* nested irq disables */     unsigned int        wake_depth; /* nested wake enables */     unsigned int        irq_count;  /* For detecting broken IRQs */     unsigned long       last_unhandled; /* Aging timer for unhandled count */     unsigned int        irqs_unhandled;     u64         random_ip;     raw_spinlock_t      lock;     struct cpumask      *percpu_enabled; #ifdef CONFIG_SMP     const struct cpumask    *affinity_hint;     struct irq_affinity_notify *affinity_notify; #ifdef CONFIG_GENERIC_PENDING_IRQ     cpumask_var_t       pending_mask; #endif #endif     unsigned long       threads_oneshot;     atomic_t        threads_active;     wait_queue_head_t       wait_for_threads; #ifdef CONFIG_PROC_FS     struct proc_dir_entry   *dir; #endif     int         parent_irq;     struct module       *owner;     const char      *name; } ____cacheline_internodealigned_in_smp;

　　

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