Re: [PATCH v10 1/3] iommu: Enhance IOMMU default DMA mode build options

[John Garry]

> >   
> >   	  If unsure, say N here.
> >   
> > +choice
> > +	prompt "IOMMU default DMA mode"
> > +	depends on IOMMU_API
>
> config INTEL_IOMMU
>          depends on PCI_MSI && ACPI && (X86 || IA64)
>
> config AMD_IOMMU
>          depends on X86_64 && PCI && ACPI && HAVE_CMPXCHG_DOUBLE
>
> config ARM_SMMU_V3
>          depends on ARM64
>
> "depends on ARM_SMMU_V3 || INTEL_IOMMU || AMD_IOMMU" may need to be added, because it doesn't work on other platforms.
>
> or "depends on X86 || IA64 || X86_64 || ARM64"

I suppose so. But I don't think that any other archs use the value from 
iommu_dma_strict anyway.

> > +
> > +	default IOMMU_DEFAULT_STRICT
> > +	help
> > +	  This option allows an IOMMU DMA mode to be chosen at build time, to
> > +	  override the default DMA mode of each ARCH, removing the need to
> > +	  pass in kernel parameters through command line. It is still possible
> > +	  to provide ARCH-specific or common boot options to override this
> > +	  option.
> > +
> > +	  If unsure, keep the default.
> > +
> > +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.
> > +
> > +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.
> > +
> > +endchoice
> > +
> >   config OF_IOMMU
> >   	def_bool y
> >   	depends on OF && IOMMU_API
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 966426a96520..177b0dafc535 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -29,7 +29,8 @@ static struct kset *iommu_group_kset;
> >   static DEFINE_IDA(iommu_group_ida);
> >   
> >   static unsigned int iommu_def_domain_type __read_mostly;
> > -static bool iommu_dma_strict __read_mostly = true;
> > +static bool iommu_dma_strict __read_mostly =
> > +			IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>
> Currently, a maximum of 100 columns are allowed in a row.

Sure, but some people still prefer limiting to 80, and codingstyle
doc mentions a preference for 80.

But if you really think I should change, then that's ok.

Thanks,
John