Re: [PATCH v12 3/5] iommu/vt-d: Add support for IOMMU default DMA mode build options

[Robin Murphy]

On 2021-06-15 08:26, Lu Baolu wrote:
> Hi John,
>
> On 6/14/21 4:03 PM, John Garry wrote:
> > On 12/06/2021 03:14, Lu Baolu wrote:
> > > On 2021/6/11 20:20, John Garry wrote:
> > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > > > index 2a71347611d4..4467353f981b 100644
> > > > --- a/drivers/iommu/Kconfig
> > > > +++ b/drivers/iommu/Kconfig
> > > > @@ -94,6 +94,7 @@ choice
> > > >       prompt "IOMMU default DMA mode"
> > > >       depends on IOMMU_DMA
> > > > +    default IOMMU_DEFAULT_LAZY if INTEL_IOMMU
> > > >       default IOMMU_DEFAULT_STRICT
> > >
> > > If two default values are different. Which one will be overridden?
> >
> > If I understand your question correctly, I think you are asking if 
> > both are set:
> > CONFIG_IOMMU_DEFAULT_LAZY=y
> > CONFIG_IOMMU_DEFAULT_STRICT=y
> >
> > If this happens, then make defconfig complains about both being set, 
> > and selects the 2nd, whatever that is.
>
> On x86, Intel or AMD, this will be
>
>      prompt "IOMMU default DMA mode"
>        depends on IOMMU_DMA
>        default IOMMU_DEFAULT_LAZY
>        default IOMMU_DEFAULT_STRICT
>
> which will be default, LAZY or STRICT? Will it cause complains?

See Documentation/kbuild/kconfig-language.rst:

  A config option can have any number of default values. If multiple
  default values are visible, only the first defined one is active.


Robin.