Jan Kiszka wrote:
Anders Blomdell wrote:

While looking into how to implement sharing of interrupts between
realtime and non-realtime domains (and applying Wolfgang Grandegger's
patch [https://mail.gna.org/public/xenomai-core/2006-01/msg00233.html],
which is necessary to make XN_ISR_ENABLE work at all on the PowerPC
platform), I'm beginning to think that XN_ISR_CHAINED and XN_ISR_ENABLE
are mutually exclusive, since if both are set, desc->handler->end will
be called twice:

 1. When the realtime isr handler returns
 2. When the Linux domain calls it in __do_IRQ

Yes, those bits are semantically exclusive. Actually, I think passing
both bits could even cause deadlocks if the RT-IRQ is raised again
before the non-RT handler got a chance to clear the IRQ source in hardware.
My impression as well, but it's nowhere documented, nor enforced in the code.

In the solution I have in mind at the moment, I will:

 1. Add an extra iend handler argument to xnintr_init
 2. If XN_ISR_ENABLE is returned from the isr handler,
    replace desc->handler->end with the user supplied
    iend handler.

Hereby I hope to be able to handle interrupts shared between realtime
and non-realtime domain, without having the realtime domain wait for all
non-realtime interrupts to finish. This is the scenario I'm thinking of:

 1. A non-RT interrupt occurs
 2. The (RT) isr handler detects the non-RT interrupt,
    disables further non-RT interrupts on that irq-vector, replaces

This remains vague to me. How precisely will you disable? I guess at
hardware level, i.e. in a (non-RT) device-specific way: switch off the
bit in some hardware register that says "this device can produce IRQs",

    desc->handler->end with the user supplied iend handler,
 3. RT interrupts are serviced by the (RT) isr handler,
    returns XN_ISR_ENABLE
 4. The Linux domain get a chance to run the chained interrupt,
    and eventually calls desc->handler->end (supplied iend handler)
 5. The iend handler reenables non-RT interrupts.

Then this would switch on that bit again? Note that this may require to
synchronise the hardware access with parts of the non-RT driver.
If the non-RT driver sets that bit in its ISR routine, yes. I have the (overly optimistic?) view that the non-RT ISR only does whatever is necessary to clear the interrupt and leaves the enable/disable bits untouched.

 Meanwhile I recalled that my hack to realise IRQ sharing between a RT
device and a non-RT eepro100 is filed on a public archive:

Thanks, I'll take a look at it.


Anders Blomdell

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