Re: [PATCH v2 09/11] iommu/vt-d: Remove commented code

[Lu Baolu]

On 2/16/22 11:45 AM, Tian, Kevin wrote:
> > From: Christoph Hellwig<hch@xxxxxx>
> > 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@xxxxxx>
> >
> > 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.

Emm, I have no idea either. Let me check it with the architecture
experts.

> 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.

Best regards,
baolu