xen/timer: make xen timer optional

[ehem_freebsd_m5p.com]

Summary

The timer is not used on ARM.

Adapted-to-HEAD-by: Elliott Mitchell <[e-mail]>

[royger]

Some minor comments.

sys/amd64/conf/GENERIC

383–384

I don't think XENHVM strictly depends on xentimer (as it does on xenpci). It's the other way around, xentimer depends on XENHVM, but you should be able to build a kernel with XENHVM but without xentimer.

387

Could you please append a comment with 'Xen x86 PV timer device' , like it's done for the other lines?

[ehem_freebsd_m5p.com]

Getting one of the adjustments in.

[ehem_freebsd_m5p.com]

The one comment is done. Thinking about the wording for the other a bit more. The comment came from Julien Grall's original patch, so I can believe time having changed things or the original thinking being mistaken.

[ehem_freebsd_m5p.com]

sys/amd64/conf/GENERIC

383–384

I don't think XENHVM strictly depends on xentimer (as it does on xenpci). It's the other way around, xentimer depends on XENHVM, but you should be able to build a kernel with XENHVM but without xentimer.

Could I have some certainty here? Does an x86 kernel built with XENHVM, but xentimer disabled boot successfully?

[royger]

sys/amd64/conf/GENERIC

383–384

Yes, it will just use another timer, there are plenty on HVM guests, and on PVH it should resort to the local APIC timer.

[ehem_freebsd_m5p.com]

Adjust comment along proposed line. Hopefully this language works.

[royger]

sys/conf/files

3552–3553

I've slightly changed this to make it depend on both xentimer and xenhvm (since trying to build the timer without the rest of xenhvm won't work anyway).