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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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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Buildable 70200
Build 67083: arc lint + arc unit

Event Timeline

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

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

Herald added a reviewer: andrew. · View Herald TranscriptDec 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.Thu, Jan 22, 8:57 PM

ehem_freebsd_m5p.com added a subscriber: royger.Thu, Jan 22, 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.