Title: [6830] trunk/arch/blackfin/mach-common/interrupt.S: Blackfin: document __ipipe_call_irqtail
- Revision
- 6830
- Author
- vapier
- Date
- 2009-06-22 13:21:04 -0500 (Mon, 22 Jun 2009)
Log Message
Blackfin: document __ipipe_call_irqtail
Modified Paths
Diff
Modified: trunk/arch/blackfin/mach-common/interrupt.S (6829 => 6830)
--- trunk/arch/blackfin/mach-common/interrupt.S 2009-06-22 18:20:48 UTC (rev 6829)
+++ trunk/arch/blackfin/mach-common/interrupt.S 2009-06-22 18:21:04 UTC (rev 6830)
@@ -261,6 +261,31 @@
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;
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