Dmitry Adamushko wrote: >> For RTDM I'm now almost determined to rework the API in way that only >> HANDLED/UNHANDLED (or what ever their names will be) get exported, any >> additional guru features will remain excluded as long as we have no >> clean usage policy for them. > > Good. Then let's go for > > HANDLED, UNHANDLED - we may consider them even as 2 scalar values
Ok, just avoid the 0.
>
> +
>
> NOENABLE, CHAINED - additional bits.
>
> They are not encouraged to be used with shared interrupts
> (explained in docs + debug messages when XENO_OPT_DEBUG is on).
>
> Any ISR on the shared irq line should "understand" that it's
> just one among the equals. That said, it should not do anything
> that may affect other ISRs and not require any special treatment
> (like CHAINED or NOENABLE).
> If it wants it indeed, then don't declare itself as SHARED.
>
> We may come back to the topic about possible return values of ISRs
> a bit later maybe having got more feedback (hm.. hopefully)
> on shared irq support.
>
>
>>>> But the later one is not only about enabling the line, but
>>>> on some archs - about .end-ing it too (sending EOI).
>>>>
>>>> And to support HANDLED_NOENABLE properly, those 2 have to be
>>>> decoupled, i.e.
>>>> EOI should always be sent from xnintr_shirq_handler().
>>> But the one returning HANDLED_NOENABLE is likely to leave the interrupt
>>> asserted, hence we can't EOI at this point (unless NO_ENABLE means
>>> DISABLE).
>> I guess this is what Dmitry meant: explicitly call disable() if one or
>> more ISRs returned NOENABLE - at least on archs where end != enable.
>> Will this work? We could then keep on using the existing IRQ-enable API
>>from bottom-half IRQ tasks.
>
> Almost.
>
> Let's consider the following only as anorther way of doing some things;
> I don't propose to implement it, it's just to illustrate my thoughts.
> So one may simply ski-skip-skip it :o)
>
> Let's keep in mind that what is behind .end-ing the IRQ line depends on
> archs.
> Sometimes end == enable (EOI was sent on .ack step), while in other cases
> end == send_EOI [+ re-enabling].
>
> But anyway, all ISRs are running with a given IRQ line disabled.
>
> Supported values : HANDLED, UNHANDLED, PROPAGATE.
>
> nucleus :: xnintr_irq_handler()
> {
> ret = 0;
>
> ...
>
> for each isr in isr_list[ IRQ ]
> {
> temp = isr->handler();
>
> if (temp > ret)
> ret = temp;
> }
>
> if (ret == PROPAGATE)
> {
> // quite dengerous with shared interrupts, be sure you understand
> // what you are doing!
>
> xnarch_chain_irq(irq); // will be .end-ed in Linux domain
> }
> else
> {
> // HANDLED or UNHANDLED
>
> xnarch_end_irq();
> }
>
> ...
>
> }
>
> ENABLE or NOENABLE is missing? Nop.
>
> let's say we have 2 rt-ISRs :
>
> isr1 : HANDLED
> isr2 : HANDLED + WISH
>
> WISH == I want the IRQ line remain disabled until later
> (e.g. bottom half in rt_task will enable it)
>
> How may isr2 express this WISH? Simply, xnarch_irq_disable/enable() should
> support an internal counter that allows them to be called in a nested way.
>
> So e.g. if there are 2 consecutive calls to disable_irq(), then
> 2 calls to enable_irq() are needed to really enable the IRQ line.
>
> This way, the WISH is only about directly calling xnarch_irq_disable() in
> isr2
> and there is no need in ENABLE or NOENABLE flags.
>
> This way, PROPAGATE really means NOEND - the IRQ will be .end-ed in Linux
> domain;
> while WISH==NOENABLE - has nothing to do with sending EOI, but only with
> enabling/disabling the given IRQ line.
>
> Yes, if one isr (or a few) defers the IRQ line enabling until later, it will
> affect
> all others ISR => all interrupts are temporary not accepted on this line.
> This scenario is possible under Linux, but should be used with even more
> care in real-time system. At least, this way HANDLED_NOENABLE case works
> and doesn't lead to lost interrupts on some archs.
>
> Moreover, it avoids the need for ENABLE flag even in non-shared interrupt
> case.
>
Yep, really looks like this is the best way to go.
Jan
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