Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options

[John Garry]

> > > -config IOMMU_DEFAULT_PASSTHROUGH
> > > -    bool "IOMMU passthrough by default"
> > > +choice
> > > +    prompt "IOMMU default DMA mode"
> > >      depends on IOMMU_API
> > > -        help
> > > -      Enable passthrough by default, removing the need to pass in
> > > -      iommu.passthrough=on or iommu=pt through command line. If this
> > > -      is enabled, you can still disable with iommu.passthrough=off
> > > -      or iommu=nopt depending on the architecture.
> > > +    default IOMMU_DEFAULT_STRICT
> > > +    help
> > > +      This option allows IOMMU DMA mode to be chose at build time, to
> >
> > As before:
> > /s/chose/chosen/, /s/allows IOMMU/allows an IOMMU/
> I'm sorry that the previous version was not modified.
>
> > > +      override the default DMA mode of each ARCHs, removing the need to
> >
> > Again, as before:
> > ARCHs should be singular
> OK
>
> > > +      pass in kernel parameters through command line. You can still use
> > > +      ARCHs specific boot options to override this option again.

*

> > > +
> > > +config IOMMU_DEFAULT_PASSTHROUGH
> > > +    bool "passthrough"
> > > +    help
> > > +      In this mode, the DMA access through IOMMU without any addresses
> > > +      translation. That means, the wrong or illegal DMA access can not
> > > +      be caught, no error information will be reported.
> > >
> > >        If unsure, say N here.
> > >
> > > +config IOMMU_DEFAULT_LAZY
> > > +    bool "lazy"
> > > +    help
> > > +      Support lazy mode, where for every IOMMU DMA unmap operation, the
> > > +      flush operation of IOTLB and the free operation of IOVA are deferred.
> > > +      They are only guaranteed to be done before the related IOVA will be
> > > +      reused.
> >
> > why no advisory on how to set if unsure?
> Because the LAZY and STRICT have their own advantages and disadvantages.
>
> Should I say: If unsure, keep the defaultã

Maybe. So you could put this in the help for the choice, * above, and 
remove the advisory on IOMMU_DEFAULT_PASSTHROUGH.

However the maintainer may have a different view.

Thanks,
John

> > > +
> > > +config IOMMU_DEFAULT_STRICT
> > > +    bool "strict"
> > > +    help
> > > +      For every IOMMU DMA unmap operation, the flush operation of IOTLB and
> > > +      the free operation of IOVA are guaranteed to be done in the unmap
> > > +      function.
> > > +
> > > +      This mode is safer than the two above, but it maybe slower in some
> > > +      high performace scenarios.
> >
> > and here?