Messages in this thread | | | Subject | Re: Using irq-crossbar.c | From | Mason <> | Date | Sun, 12 Jun 2016 15:50:22 +0200 |
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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.)
> 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?
>> Is this Doxygen format? Is there a make target to generate >> some documentation? > > Try "make help".
Documentation targets: Linux kernel internal documentation in different formats: htmldocs - HTML pdfdocs - PDF psdocs - Postscript xmldocs - XML DocBook mandocs - man pages installmandocs - install man pages generated by mandocs cleandocs - clean all generated DocBook files
>>> - 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)
(Our previous intc had N=64 and M=3; the new one has N=128 and M=24)
Regards.
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