Re: [PATCH v2 1/1] iommu/vt-d: Add Kconfig option to enable/disable scalable mode

[Lu Baolu]

Hi,

On 11/11/19 10:58 AM, Qian Cai wrote:
> > On Nov 8, 2019, at 10:43 PM, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
> >
> > +config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
> > +    prompt "Enable Intel IOMMU scalable mode by default"
> > +    depends on INTEL_IOMMU
> > +    help
> > +      Selecting this option will enable the scalable mode if
> > +      hardware presents the capability. If this option is not
> > +      selected, scalable mode support could also be enabled
> > +      by passing intel_iommu=sm_on to the kernel.
> > +
>
> Does it also make sense to mention which hardware presents this capability or how to check it?

The scalable mode is defined in VT-d 3.0. The scalable mode capability
could be checked by reading /sys/devices/virtual/iommu/dmar*/intel-
iommu/ecap. It's currently not friendly for reading. You need to decode
it according to the spec.

Best regards,
baolu