probe_irq_on, probe_irq_off - safe probing for IRQs

SYNOPSIS

       #include <linux/interrupt.h>

       unsigned long probe_irq_on(void)
       int probe_irq_off(unsigned long irqs);

DESCRIPTION

   Usage
       probe_irq_on()  turns  on  IRQ  detection.  It operates by
       enabling all interrupts  which  have  no  handlers,  while
       keeping  the handlers for those interrupts NULL.  The ker­
       nel's generic  interrupt  handling  routine  will  disable
       these   IRQs  when  an  interrupt  is  received  on  them.
       probe_irq_on() adds each of these IRQ numbers to a  vector
       which  it  will  return.  It waits approximately 100ms for
       any spurious interrupts that may occur,  and  masks  these
       from  its  vector;  it  then  returns  this  vector to its
       caller.

       probe_irq_off() tests an internal  list  of  enabled  IRQs
       against  its  irqs  parameter,  which  should be the value
       returned by the last probe_irq_on().  This function  basi­
       cally  detects which IRQs have been switched off, and thus
       which ones have received interrupts.

   Example
       This explanation may seem a bit confusing, so here  is  an
       example  of  code the mythical FUBAR 2000 driver could use
       to probe for IRQs:

              unsigned long irqs;
              int irq;

              irqs = probe_irq_on();

              outb(FB2K_GIVE_ME_AN_INTERRUPT_OR_GIVE_ME_DEATH,
                   FB2K_CONTROL_PORT);
                /* the interrupt could take a while to occur */
              udelay(1000);

              irq = probe_irq_off(irqs);

              if (irq == 0) {
                   printk("fb2k: could not detect IRQ.\n");
                   printk("fb2k: Installation failed.\n");
              } else if (irq == -1) {
                   printk("fb2k: multiple IRQs detected.\n");
                   printk("fb2k: Installation failed.\n");
              } else {
                   fb2k_dev->irq = irq;

RETURN VALUE

       probe_irq_on() returns a  bitmap  of  all  unhandled  IRQs
       (except  those  which  are receiving spurious interrupts).
       This value should only be used as a parameter to the  next
       call to probe_irq_off().

       probe_irq_off() returns the IRQ number of whichever unhan­
       dled interrupt has occurred since the last probe_irq_on().
       If  no interrupts have occurred on any of the marked IRQs,
       0 is returned; if interrupts have occurred  on  more  than
       one of these IRQs, -1 is returned.

AVAILABILITY

       Linux  1.2+.   These  functions are not available on m68k-
       based machines.

SEE ALSO

       request_irq(9)

       arch/*/kernel/irq.c

AUTHOR

       Neil Moore <amethyst@maxwell.ml.org>

BUGS

       As mentioned above, these functions are not  available  on
       m68k-based machines.

       This manpage is way too confusing.