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SubjectRE: [PATCH v2 09/11] iommu/vt-d: Remove commented code
Date
> From: Christoph Hellwig <hch@lst.de>
> Sent: Monday, February 14, 2022 3:34 PM
>
> On Mon, Feb 14, 2022 at 10:57:02AM +0800, Lu Baolu wrote:
> > This removes unnecessary commented code.
>
> Removing dead code is always good:
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
>
> But someone might really want to take a look if draining makes sense here
> or not.

Looks that dead code has been there since intel-iommu driver was
firstly introduced in 2007. I don't know whether we can dig out
the reason (Baolu, can you have a check?) why it's only special
cased for read draining but not write draining. I cannot find any
such recommendation from VT-d spec.

Looking at VT-d spec it stated that since VT-d major version 2
drain is conducted automatically by hardware and above flags
are essentially ignored.

Given that possibly a safer option is to always set read/write
draining flags before version 2 and skip it after.

Thanks
Kevin

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