On 2014/11/7 0:34, Marc Zyngier wrote: > 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. Hi Marc, It works exactly in this way:) > > 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. irq_alloc_info is newly introduced for hierarchy irqdomain on x86. Regards! Gerry > > I'll try to hack something with my current ITS driver and come back with > the results. > > Thanks, > > M. > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
