Anders Blomdell wrote: > For the last few days, I have tried to figure out a good way to share > interrupts between RT and non-RT domains. This has included looking > through Dmitry's patch, correcting bugs and testing what is possible in > my specific case. I'll therefore try to summarize at least a few of my > thoughts. > > 1. When looking through Dmitry's patch I get the impression that the > iack handler has very little to do with each interrupt (the test > 'prev->iack != intr->iack' is a dead giveaway), but is more of a > domain-specific function (or perhaps even just a placeholder for the > hijacked Linux ack-function). > > > 2. Somewhat inspired by the figure in "Life with Adeos", I have > identified the following cases: > > irq K | ----------- | ---o | // Linux only > ... > irq L | ---o | | // RT-only > ... > irq M | ---o------- | ---o | // Shared between domains > ... > irq N | ---o---o--- | | // Shared inside single domain > ... > irq O | ---o---o--- | ---o | // Shared between and inside single > domain > > Xenomai currently handles the K & L cases, Dmitrys patch addresses the N > case, with edge triggered interrupts the M (and O after Dmitry's patch) > case(s) might be handled by returning RT_INTR_CHAINED | RT_INTR_ENABLE > from the interrupt handler, for level triggered interrupt the M and O > cases can't be handled.
I guess you mean it the other way around: for the edge-triggered cross-domain case we would actually have to loop over both the RT and the Linux handlers until we are sure, that the IRQ line was released once. Luckily, I never saw such a scenario which were unavoidable (it hits you with ISA hardware which tend to have nice IRQ jumpers or other means - it's just that you often cannot divide several controllers on the same extension card IRQ-wise apart). > > If one looks more closely at the K case (Linux only interrupt), it works > by when an interrupt occurs, the call to irq_end is postponed until the > Linux interrupt handler has run, i.e. further interrupts are disabled. > This can be seen as a lazy version of Philippe's idea of disabling all > non-RT interrupts until the RT-domain is idle, i.e. the interrupt is > disabled only if it indeed occurs. > > If this idea should be generalized to the M (and O) case(s), one can't > rely on postponing the irq_end call (since the interrupt is still needed > in the RT-domain), but has to rely on some function that disables all > non-RT hardware that generates interrupts on that irq-line; such a > function naturally has to have intimate knowledge of all hardware that > can generate interrupts in order to be able to disable those interrupt > sources that are non-RT. > > If we then take Jan's observation about the many (Linux-only) interrupts > present in an ordinary PC and add it to Philippe's idea of disabling all > non-RT interrupts while executing in the RT-domain, I think that the > following is a workable (and fairly efficient) way of handling this: > > Add hardware dependent enable/disable functions, where the enable is > called just before normal execution in a domain starts (i.e. when > playing back interrupts, the disable is still in effect), and disable is > called when normal domain execution end. This does effectively handle > the K case above, with the added benefit that NO non-RT interrupts will > occur during RT execution. > > In the 8259 case, the disable function could look something like: > > domain_irq_disable(uint irqmask) { > if (irqmask & 0xff00 != 0xff00) { > irqmask &= ~0x0004; // Cascaded interrupt is still needed > outb(irqmask >> 8, PIC_SLAVE_IMR); > } > outb(irqmask, PIC_MASTER_IMR); > } > > If we should extend this to handle the M (and O) case(s), the disable > function could look like: > > domain_irq_disable(uint irqmask, shared_irq_t *shared[]) { > int i; > > for (i = 0 ; i < MAX_IRQ ; i++) { > if (shared[i]) { > shared_irq_t *next = shared[i]; > irqmask &= ~(1<<i); > while (next) { > next->disable(); > next = next->next; > } This obviously means that all non-RT IRQ handlers sharing a line with the RT domain would have to be registered in that shared[]-list. This gets close to my old suggestion. Just raises the question how to organise these interface, both on the RT and the Linux side. > } > } > if (irqmask & 0xff00 != 0xff00) { > irqmask &= ~0x0004; // Cascaded interrupt is still needed > outb(irqmask >> 8, PIC_SLAVE_IMR); > } > outb(irqmask, PIC_MASTER_IMR); > } > > An obvious optimization of the above scheme, is to never call the > disable (or enable) function for the RT-domain, since there all > interrupt processing is protected by the hardware. Another point is to avoid that looping over disable handlers for IRQs of the K case. Otherwise, too many device-specific disable handlers had to be implemented even if only a single Linux device hogs a RT IRQ. > > Comments, anyone? > I see your need, we just have to keep in mind that we are currently discussing the corner case (shared RT/non-RT IRQs) of the corner case (shared RT IRQs). Whatever will be defined, the normal use case should define how an efficient interface has to look like. Or we have to add a lot of #ifdef's... Jan
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