linuxkpi: Acquire giant when adding/removing i2c adapters

[manu]

Summary

We need Giant as we run in a taskqueue_thread via linux_work.
This fix detaching amdgpu and i915kms.

Sponsored by: Beckhoff Automation GmbH & Co. KG

[manu]

I don't know why I don't need this but looking at the device_delete_child and bus_generic_attach code we need giant.
There is a report of this function failing https://github.com/freebsd/drm-kmod/issues/154 .

[• hselasky]

If I'm not mistaken you should just bus_topo_lock() and bus_topo_unlock() instead of referring Giant directly!

[manu]

Use bus_topo_lock/unlock

[manu]

In D35478#804573, @hselasky wrote:

If I'm not mistaken you should just bus_topo_lock() and bus_topo_unlock() instead of referring Giant directly!

Indeed, fixed now.

[imp]

Nothing new in the tree should refer to Giant... I'll have to see if we can poison that to keep it from proliferating.
The bus_topo_* functions were a part of that work, and appear to be used here correctly.