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 18:31:09 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off"

On Tue, Sep 23, 2008 at 12:25:23AM +0900, FUJITA Tomonori wrote:
> I don't think that users need to have iommu=calgary parameter to use
> calgary IOMMU by default. If you enable CONFIG_CALGARY_IOMMU,
> CALGARY_IOMMU_ENABLED_BY_DEFAULT is also enabled by default. If a
> kernel finds calgary IOMMU, the kernel uses it by default.
> 
> It's also consistent with how SWIOTLB. Users don't need iommu=soft
> parameter to enable SWIOTLB. A kernel enables SWIOTLB automatically
> when necessary.

Yes. The parameters are usefull if a user wants to enable a specific
IOMMU implementation. The user could be an IOMMU developer testing
changes in a special implementation the kernel would not choose by
default on his machine.
I like Ingo's idea here. Lets do boths, implementing iommu=$type to
force a specific iommu implementation and $(type)_iommu=off to disable
one.

> Well, this is the problem about the IOMMUs parameters. The IOMMUs
> parameters are too complicated for everyone.

Not so complicated that they can't be understood. But if you have a
proposal how the command line parameters for iommus may look like, send
it. I like join that discussion about the interface.

Joerg

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