Messages in this thread | | | Date | Thu, 6 Nov 2014 11:42:32 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [V10 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m MSI(-X) |
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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 ]
If you look at Jiangs x86 implementation it does exactly that.
[ MSI ] ---> [ Vector ]
[ MSI ] ---> [ Remap ] ---> [ Vector ]
And because ARM has this intermediate layer of GIC-MSI you need to represent it in the hierarchy whether you like it or not. If you'd try to bolt the GIC-MSI magic into the MSI layer itself, then interrupt remapping would never work.
Thanks,
tglx
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