Messages in this thread | | | Subject | Re: Using irq-crossbar.c | From | Marc Zyngier <> | Date | Mon, 13 Jun 2016 08:58:33 +0100 |
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On 12/06/16 14:50, Mason wrote: > On 12/06/2016 12:00, Marc Zyngier wrote: > >> Mason wrote: >> >>> The problem with some Linux APIs is that they're logical and obvious >>> to people who've been using them for years. For newcomers, it's not >>> always so obvious. >>> >>> In this specific instance, the problem statement seems rather simple, >>> on the surface. An interrupt controller, X=0..127 lines in, Y=0..23 >>> lines out (connected to GIC interrupt lines 0..23) and "all" we need >>> is a way to map Xs to Ys. >>> >>> As a first order approximation, it's enough to map all Xs to 0. >>> And provide a way for the kernel to check the registers containing >>> the bit-vectors indicating which interrupt(s) fired. >> >> If that's what your hardware is, then you are taking the wrong >> approach. The irq-crossbar driver does not do that at all: it has x >> inputs and y outputs, but connects exactly *one input to one output*. >> No multiplexing. > > Connecting one input to one output is possible iff x=y right? > (In other words, a bijection.)
It is *always* possible to connect anything to anything else. You were assuming that this particular driver was fitting your particular case, and it is obvious that it is not (iow: the crossbar transformation cannot be surjective).
>> And the hierarchical domain infrastructure enforces a similar property: >> a Linux interrupt is dealt with at each level of the hierarchy without >> multiplexing: the "irq" is the same, while the "hwirq" varies to >> reflect the "input pin" for a given interrupt controller. >> >> In your particular case, you have an evolved chained interrupt >> controller, and nothing else. > > Is it possible to support such an "evolved chained intc" through DT only, > or does it require a few function calls from driver code?
There is no such thing as "DT only". You will have to do some actual irqchip development.
>>>> - You've changed the default interrupt controller to be your crossbar. >>>> Which means that all the sub-nodes are inheriting it. Have you >>>> checked that this was valid for all of these nodes? >>> >>> I'm not sure I follow. All platform interrupts flow into the platform >>> controller. Maybe other platforms have more complex setups, with >>> several cascaded controllers? >> >> Most embedded platforms do. > > My imagination is lacking, I don't see why it needs to be more > complex than N platform input lines, and M output lines feeding > into the GIC (with M <= N)
It is not more complex. It is different.
M. -- Jazz is not dead. It just smells funny...
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