Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH v2 09/11] iommu/vt-d: Remove commented code | Date | Wed, 16 Feb 2022 03:45:33 +0000 |
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> 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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