Blackfin: document __ipipe_call_irqtail

ENDPROC(_evt_system_call)

#ifdef CONFIG_IPIPE

/*

 * __ipipe_call_irqtail: lowers the current priority level to EVT15

 * before running a user-defined routine, then raises the priority

 * level to EVT14 to prepare the caller for a normal interrupt

 * return through RTI.

 *

 * We currently use this facility in two occasions:

 *

 * - to branch to __ipipe_irq_tail_hook as requested by a high

 *   priority domain after the pipeline delivered an interrupt,

 *   e.g. such as Xenomai, in order to start its rescheduling

 *   procedure, since we may not switch tasks when IRQ levels are

 *   nested on the Blackfin, so we have to fake an interrupt return

 *   so that we may reschedule immediately.

 *

 * - to branch to sync_root_irqs, in order to play any interrupt

 *   pending for the root domain (i.e. the Linux kernel). This lowers

 *   the core priority level enough so that Linux IRQ handlers may

 *   never delay interrupts handled by high priority domains; we defer

 *   those handlers until this point instead. This is a substitute

 *   to using a threaded interrupt model for the Linux kernel.

 *

 * r0: address of user-defined routine

 * context: caller must have preempted EVT15, hw interrupts must be off.

 */

ENTRY(___ipipe_call_irqtail)

	p0 = r0;

	r0.l = 1f;