On Tue, Jan 22, 2013 at 07:29:01PM +0000, Jason Gunthorpe wrote: > 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 :) Thanks for this. I believe Thierry may be working on improving the MSI API - so perhaps we can see where that takes us. Andrew Murray -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
