4.5 只在head domain注册的设备中断处理流程

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4.5 只在head domain注册的设备中断

哪些设备会只在head domain Xenomai中注册中断呢？这就需要说一下Xenomai中的实时驱动模型（RTDM）。

在J. Kiszka的论文《The Real-Time Driver Model and First Applications》中指出：自从所谓的双内核硬实时Linux扩展（如RTLinux[1]和RTAI[2]）被引入以来，已经开发了大量的驱动程序。仅举几例，就有像Comedi[3]、rtcan[4]或rtcom[5]这样的独立厂商项目，以及厂商提供的驱动包[7, 6]。尽管这些驱动程序针对类似的硬件，但到目前为止，在统一的应用程序编程接口上投入的努力很少。大多数驱动程序都定义了自己的库式API，这阻碍了硬件的轻松替换，因为应用程序软件需要适应新硬件的驱动程序。实时驱动模型（RTDM）旨在统一在实时Linux下开发设备驱动程序及其相关应用程序的接口。

在Xenomai 3中，已经包含了一些RTDM设备驱动，例如can、net、spi、serial、gpio等设备驱动。这些设备注册中的接口是rtdm_irq_request。

以drivers/xenomai/net/drivers/macb.c为例，驱动加载后，匹配到对应的platform_device（.name = “macb”），调用macb_probe执行设备初始化。

第1654行，通过platform_get_irq->of_irq_get获取Linux virq。

第1657行，调用rtdm_irq_request为virq注册中断处理程序macb_interrupt。先埋个伏笔，macb_interrupt的返回值为RTDM_IRQ_HANDLED。注意rtdm_irq_request的第一个参数，它是一个rtdm_irq_t类型（即struct xnintr）的数据结构实例。

typedef struct xnintr rtdm_irq_t;

struct xnintr {
#ifdef CONFIG_XENO_OPT_SHIRQ
    /** Next object in the IRQ-sharing chain. */
    struct xnintr *next;
#endif
    /** Number of consequent unhandled interrupts */
    unsigned int unhandled;
    /** Interrupt service routine. */
    xnisr_t isr;
    /** User-defined cookie value. */
    void *cookie;
    /** runtime status */
    unsigned long status;
    /** Creation flags. */
    int flags;
    /** IRQ number. */
    unsigned int irq;
    /** Interrupt acknowledge routine. */
    xniack_t iack;
    /** Symbolic name. */
    const char *name;
    /** Descriptor maintenance lock. */
    raw_spinlock_t lock;
#ifdef CONFIG_XENO_OPT_STATS_IRQS
    /** Statistics. */
    struct xnirqstat *stats;
#endif
};

接着分析rtdm_irq_request，它经过层层调用走到ipipe_request_irq，向head domain Xenomai注册中断处理程序。但是它注册的中断程序是xnintr_irq_handler，为啥？

第1489行，在xnintr_init中，对irq_handle进行初始化，其中irq成员初始化为virq，isr成员指向中断处理程序macb_interrupt。

int xnintr_init(struct xnintr *intr, const char *name,
		unsigned int irq, xnisr_t isr, xniack_t iack,
		int flags)
{
	secondary_mode_only();

	if (irq >= IPIPE_NR_IRQS)
		return -EINVAL;

	intr->irq = irq;
	intr->isr = isr;
	intr->iack = iack;
	intr->cookie = NULL;
	intr->name = name ? : "<unknown>";
	intr->flags = flags;
	intr->status = _XN_IRQSTAT_DISABLED;
	intr->unhandled = 0;
	raw_spin_lock_init(&intr->lock);
#ifdef CONFIG_XENO_OPT_SHIRQ
	intr->next = NULL;
#endif
	alloc_irqstats(intr);

	return 0;
}
EXPORT_SYMBOL_GPL(xnintr_init);

第1493行，继续调用xnintr_attach。

第586行，此处向head domain Xenomai注册中断处理程序是xnintr_irq_handler，把指针intr（指向irq_handle）作为xnintr_irq_handler执行的参数。

在xnintr_irq_handler执行的过程中，先是执行intr->isr即macb_interrupt，然后根据macb_interrupt的返回值，判断是否要传递中断到root domain。只有当返回值为XN_IRQ_PROPAGATE时，才会传递中断到root domain。

上面已经提到了，macb_interrupt的返回值是XN_IRQ_HANDLED，所有第668行不会执行，会走到第670行，结束中断。

在xnintr_init的注释中，明确写道：强烈不建议使用XN_IRQ_PROPAGATE。

/**
 * @fn int xnintr_init(struct xnintr *intr,const char *name,unsigned int irq,xnisr_t isr,xniack_t iack,int flags)
 * @brief Initialize an interrupt descriptor.
 *
 * When an interrupt occurs on the given @a irq line, the interrupt
 * service routine @a isr is fired in order to deal with the hardware
 * event. The interrupt handler may call any non-blocking service from
 * the Cobalt core.
 *
 * Upon receipt of an IRQ, the interrupt handler @a isr is immediately
 * called on behalf of the interrupted stack context, the rescheduling
 * procedure is locked, and the interrupt line is masked in the system
 * interrupt controller chip.  Upon return, the status of the
 * interrupt handler is checked for the following bits:
 *
 * - XN_IRQ_HANDLED indicates that the interrupt request was
 * successfully handled.
 *
 * - XN_IRQ_NONE indicates the opposite to XN_IRQ_HANDLED, meaning
 * that no interrupt source could be identified for the ongoing
 * request by the handler.
 *
 * In addition, one of the following bits may be present in the
 * status:
 *
 * - XN_IRQ_DISABLE tells the Cobalt core to disable the interrupt
 * line before returning from the interrupt context.
 *
 * - XN_IRQ_PROPAGATE propagates the IRQ event down the interrupt
 * pipeline to Linux. Using this flag is strongly discouraged, unless
 * you fully understand the implications of such propagation.
 *
 * @warning The handler should not use these bits if it shares the
 * interrupt line with other handlers in the real-time domain. When
 * any of these bits is detected, the interrupt line is left masked.
 *
 * A count of interrupt receipts is tracked into the interrupt
 * descriptor, and reset to zero each time such descriptor is
 * attached. Since this count could wrap around, it should be used as
 * an indication of interrupt activity only.
 *
 * @param intr The address of a descriptor the Cobalt core will use to
 * store the interrupt-specific data.
 *
 * @param name An ASCII string standing for the symbolic name of the
 * interrupt or NULL.
 *
 * @param irq The IRQ line number associated with the interrupt
 * descriptor. This value is architecture-dependent. An interrupt
 * descriptor must be attached to the system by a call to
 * xnintr_attach() before @a irq events can be received.
 *
 * @param isr The address of an interrupt handler, which is passed the
 * address of the interrupt descriptor receiving the IRQ.
 *
 * @param iack The address of an optional interrupt acknowledge
 * routine, aimed at replacing the default one. Only very specific
 * situations actually require to override the default setting for
 * this parameter, like having to acknowledge non-standard PIC
 * hardware. @a iack should return a non-zero value to indicate that
 * the interrupt has been properly acknowledged. If @a iack is NULL,
 * the default routine will be used instead.
 *
 * @param flags A set of creation flags affecting the operation. The
 * valid flags are:
 *
 * - XN_IRQTYPE_SHARED enables IRQ-sharing with other interrupt
 * objects.
 *
 * - XN_IRQTYPE_EDGE is an additional flag need to be set together
 * with XN_IRQTYPE_SHARED to enable IRQ-sharing of edge-triggered
 * interrupts.
 *
 * @return 0 is returned on success. Otherwise, -EINVAL is returned if
 * @a irq is not a valid interrupt number.
 *
 * @coretags{secondary-only}
 */