Hi Thomas, On 06/11/14 10:42, Thomas Gleixner wrote: > On Thu, 6 Nov 2014, Thomas Gleixner wrote: >> On Wed, 5 Nov 2014, Suravee Suthikulanit wrote: >>> On 11/5/2014 6:05 PM, Suravee Suthikulanit wrote: >>>> - Overall, it seems that msi_domain_alloc() could be quite different >>>> across architectures. Would it be possible to declare this function as >>>> weak, and allow arch to override (similar to arch_setup_msi_irq)? >>> >>> Actually, declaring "msi_domain_ops" as non-static, and allow other code to >>> override the .alloc and .free? >> >> Why do you want to do that? > > I know why. Because you want to spare a level of hierarchy. But thats > wrong simply because MSI itself is an interrupt chip at the device > level. > > [ MSI ] ---> [ GIC-MSI ] ---> [ GIC ] > > So the MSI level only cares about the allocation of the virq > space. GIC-MSI allocates out of the bitmap which handles the hard > wired range of MSI capable GIC interrupts and GIC handles the > underlying functionality. > > And this makes a lot of sense, if you think about interrupt > remapping. If ARM ever grows that you simply insert it into the chain: > > [ MSI ] ---> [ Remap] ---> [ GIC-MSI ] ---> [ GIC ] I think ARM has reached that stage with the ITS block in GICv3: - Each device gets programmed with a set of "event IDs" ranging from 0 to N-1, with N being the number of MSI vectors used by the device - the ITS uses both the device ID (basically the PCI requester ID) and the event ID to parse a set of software-managed tables (think page tables for interrupts). The x86 remapping thing looks quite similar to that, by reading a couple of pages from the VT-D document. So the way I understand the layout (and please correct me if I'm wrong, which is certainly the case) is that the MSI domain is entirely generic, allocates the virq, uses Remap as a parent, and uses irq_chip_compose_msi_msg to call into the parent and generate whatever goes into the MSI message. I'm still struggling a bit to see how the remapping layer can access the requester ID. x86 uses the irq_alloc_info to store that (the result of an msi_get_hwirq call), but we don't have an equivalent structure on arm/arm64. I'll try to hack something with my current ITS driver and come back with the results. Thanks, M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
