On Fri, Jun 26, 2020 at 11:10:00AM -0700, Luck, Tony wrote:
> Do we have a standard way of coding for a feature that depends on multiple
> other features? For this case the system needs to both suport the ENQCMD
> instruction, and also have kernel code that programs the IOMMU.
Yes, you need both. Consider distros enabling everything so that they
can ship a single kernel image.
> And/or guidance on when to use each of the very somewhat simlar looking
> boot_cpu_has()
> static_cpu_has()
See the comment over _static_cpu_has() in arch/x86/include/asm/cpufeature.h
In the exception path you should use the static_ variant.
> IS_ENABLED()
This is testing CONFIG_ settings, i.e., build time.
> cpu_feature_enabled()
This too, indirectly. See
arch/x86/include/asm/disabled-features.h
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
