On Wed, Sep 22, 2010 at 3:32 AM, Benjamin Herrenschmidt <b...@kernel.crashing.org> wrote: > On Tue, 2010-09-21 at 16:57 -0300, Grant Likely wrote: >> On Tue, Sep 21, 2010 at 7:25 AM, Shaju Abraham <shaju.abra...@linaro.org> >> wrote: >> > Hi Grant >> > >> > Since there does not exist a mechanism to map the hw irq to linux irq >> > on ARM (device tree), I would like to discuss with you the plans or >> > ideas to implement the same. > > Note that the powerpc hw -> linux IRQ mapping (virtualized irq numbering > scheme) is orthogonal to the device-tree. It can be used without the > device-tree and the device-tree doesn't mandate such a scheme. > > However, when used together, it does provide some nice features such as > making most cases of cascaded controllers totally trivial. > >> I don't have any immediate plans, but this topic has come up a lot in >> the last two weeks, so I guess I need to focus on it. :-) [cc'ing >> devicetree-discuss and linux-arm-kernel as well as Lorenzo and Eric >> since this is a conversation that should be had publically] >> >> > Can you share with me your thoughts on it? >> > I have browsed through the power pc code for the same. But not sure >> > the same approach is usable on ARM as well. >> >> I haven't thought deeply about the powerpc implementation of virqs to >> determine if it is suitable for other architectures or not, but the >> concept behind it is sound. We need a method of mapping controller >> specific IRQ (or hw irq) numbers into the global Linux irq space >> (referred to a virqs from this point on). First it requires a >> per-controller reference which can be a pointer to a per-controller >> data structure, or any other unique identifier. It could even be the >> interrupt controller device tree node pointer. Just so long as there >> is a reliable method to derive the virq from the controller reference >> + hw irq number. > > I like keeping it somewhat orthogonal. See how I do that on powerpc. > That way, you can still exploit it, map interrupts etc... even if your > device-tree happens to be deficient or missing. > > The main grief one could have with my scheme is the naming of irq_host > which has confused people in the past. It should probably be irq_domain > to make clear what it is. It generally have a 1:1 relationship to the > irq_chip but there are cases where that isn't the case (essentially > where you have multiple irq_chip per domain) for various reasons so it's > better to keep those separate. >
How do we handle multiplexed interrupts ? For example a single interrupt line representing multple irq sources. We have ARM systems with single interrupt line on a VIC muxed to 192 different GPIO sources (each capable of generating interrupts). For such a system the virq to hw irq mapping can get complex. > Ben. > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-ker...@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss
