linux-kernel - Re: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd

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Date:	Mon, 22 Sep 2008 16:59:53 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off"

On Mon, Sep 22, 2008 at 04:46:01PM +0200, Ingo Molnar wrote:
> 
> * Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > >     x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off
> > > 
> > >     This patch removes the amd_iommu=off kernel parameter and honors 
> > >     the generic
> > > 
> > >     iommu=off parameter for the same purpose.
> > > 
> > > 
> > > The above commit is wrong.
> > 
> > It isn't. The user normally don't care about the type of IOMMU in the 
> > system. So disabling it with iommu=off is the right way. To achieve 
> > what you want its better to add iommu=gart and iommu=amd to the option 
> > parser. This will be consistent with Calgary and SWIOTLB too.
> 
> well, what matters in the end is to have a consistent set of exclusion 
> options:
> 
>   gart_iommu=off     # disable the GART (and only that one)
>   intel_iommu=off    # disable the Intel IOMMU (and only that one)
>   amd_iommu=off      # disable AMD-IOMMU (and only that one)
> 
> then there's the all-off option:
> 
>   iommu=off          # wildcard: disable all IOMMUs
> 
> [ whether iommu=off also disables the swiotlb is a detail. ]
> 
> and we could also do the inclusive options in addition:
> 
>   iommu=gart         # use the GART as the primary IOMMU [if available]
>   iommu=amd          # use the AMD-IOMMU as the primary IOMMU [if available]
>   iommu=intel        # use the Intel IOMMU [if available]
> 
> so could we please first agree on such a specific list of generic 
> options, and then implement them consistently, while keeping legacies 
> (the ones that matter) intact as well?

Ok, having $(type)_iommu=off in addition to iommu=$type is surely a good
thing.

Joerg

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