On Thu, Jan 17, 2013 at 04:22:18PM +0000, Andrew Murray wrote: > > In either of those cases, does it make sense to use the MSI support > > outside the scope of the PCI infrastructure? That is, would devices > > other than PCI devices be able to generate an MSI? > > I've come around to your way of thinking. Your approach sounds good for > registration of MSI ops - let the RC host driver do it (it probably has its > own), or use a helper for following a phandle to get ops that are not part > of the driver. MSIs won't be used outside of PCI devices. Here is a bit of additional info on some MSI stuff.. This can be pretty complex. For instance on hyper transport systems the PCI to HT bridge has an MSI controller that maps between PCI and HT MSI formats, that mapping is configurable, so technically each brige could be considered a MSI controller. Typically the mapping controllers are all setup the same so there is not much problem with this. However *native* HT devices can (which are super rare) can use a different MSI format than PCI devices. From a linux perspective HT is just a variant of PCI. On x86 the MSI is delivered to the CPU APIC complex which converts it into a vectored interrupt - part of the value of MSI is that the MSI data can vector the interrupt to a specific CPU, or group of CPUs or whatever. Presumably SMP ARMs will evolve similar MSI based interrupt vectoring capabilities, and presumably on-chip, non-PCI peripherals will evolve options to use MSI as well (ie multi-queue ethernet). So it might be worth giving some thought to how things could migrate in that direction someday. I have a bit hacky MSI driver for Kirkwood, this work you have to generalize the interface could let me actually upstream it :) The MSI is built using the Host2CPU doorbell registers, so it is entirely unrelated to the PCI-E RC driver. However, my use of the MSI driver on kirkwood is to assign MSIs to a PCI-E device via non-standard registers, more like an on chip peripheral. This is because the Host2CPU doorbell doesn't fit 100% perfectly with the standard PCI MSI stuff, and the hardware has funny needs.. So an 'allocate a MSI interrupt' API would be snazzy too :) Jason -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
