bus: Document special ranges of IVARs
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Authored by jhb on Dec 9 2025, 8:35 PM.

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imp
andrew
manu
royger

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rG16211a5fbbaa: bus: Document special ranges of IVARs
rG6cf4e30252fe: bus: Document special ranges of IVARs

Summary

Some IVAR indices are special in that they have global meaning across
multiple buses where as other IVARs are always private to the local bus.
Try to document this a bit and add constants for the various ranges to
avoid future conflicts.

This is a no-op, but IVAR indices are now generally defined as enums
as that makes it easier to define them in terms of ranges.

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rG FreeBSD src repository

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jhb created this revision.Dec 9 2025, 8:35 PM

Owners added a reviewer: Restricted Owners Package.Dec 9 2025, 8:35 PM

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jhb requested review of this revision.Dec 9 2025, 8:35 PM

Harbormaster completed remote builds in B69156: Diff 167801.Dec 9 2025, 8:35 PM

jhb added a child revision: D54160: bus: Drop a couple of unused IVAR indices.Dec 9 2025, 8:35 PM

jhb added a parent revision: D54155: acpi_gpiobus: Reuse the existing IVAR index for an ACPI handle.Dec 9 2025, 8:35 PM

andrew added inline comments.Dec 10 2025, 2:01 PM

sys/arm64/arm64/gic_v3_var.h
114	Are you planning on MFCing this change? If not then we could just drop them.
sys/sys/bus.h
312	I don't think this is needed, the GICv3 ivars can be in the private space.

jhb added inline comments.Dec 10 2025, 4:19 PM

sys/arm64/arm64/gic_v3_var.h
114	I might MFC this change but have a followup change that can't be merged that drops unused ivars.
sys/sys/bus.h
312	I was going to ask about these as followups. For now I just want to document what is there. Can the regular GIC IVARs also be in the private space?

andrew added inline comments.Dec 10 2025, 5:10 PM

sys/arm64/arm64/gic_v3_var.h
114	It's unused from 13 so you could name it `GICV3_IVAR_UNUSED` to make it self documenting. Wouldn't it be an issue for a MFC renumbering the 1-indexed ivars to be 0-indexed?
sys/sys/bus.h
312	The regular GIC IVARs are shared between the two GIC drivers so can't be in the private space. If you keep it then the name should be `BUS_IVARS_GICV3`. I'll have a GICv5 driver in the next few weeks, but that can use the private space.

jhb added inline comments.Dec 11 2025, 5:33 PM

sys/arm64/arm64/gic_v3_var.h
114	Oh, yes, so perhaps I won't MFC after all. Still, I think removing the unused entries as a separate commit is easier to review, etc.
sys/sys/bus.h
312	Have you considered just having a single set of GIC IVARs shared by all the drivers btw?

Rename BUS_IVAR_GIC3 to BUS_IVAR_GICV3

Harbormaster completed remote builds in B69201: Diff 167920.Dec 12 2025, 2:59 PM

This looks good to me. It also shows a bit of a disconnect on how we've put the 'ranges' in different ways. A limit of 256 is likely better than 100 or 500, but honestly all are fine.

This revision is now accepted and ready to land.Jan 22 2026, 8:57 PM

ehem_freebsd_m5p.com added a subscriber: royger.Jan 22 2026, 9:38 PM

ehem_freebsd_m5p.com added inline comments.

sys/xen/xenbus/xenbusvar.h
58	After a quick glance this seems reasonable. Since I'm unfamiliar with this portion of things, @royger could you take a look?

For MFC purposes, I think I will change this to use BUS_PRIVATE_IVARS + 1 for the buses that currently start at 1 and insert a commit to renumber those. That would let me MFC this change at least.