RE: [PATCH 2/3 v6] ACPI: allow longer device IDs

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Ard Biesheuvel <ardb@kernel.org> Sent: Monday, February 28, 2022 2:22 PM
> 
> On Mon, 28 Feb 2022 at 23:14, Michael Kelley (LINUX)
> <mikelley@microsoft.com> wrote:
> >
> > From: Jason A. Donenfeld <Jason@zx2c4.com> Sent: Monday, February 28, 2022
> 1:55 PM
> > >
> > > Hi Andy,
> > >
> > > On Mon, Feb 28, 2022 at 10:28 PM Andy Shevchenko
> > > <andy.shevchenko@gmail.com> wrote:
> > > > My point is that this is clear abuse of the spec and:
> > > > 1) we have to enable the broken, because it is already in the wild with
> > > >    the comment that this is an issue
> > > >
> > > > AND
> > > >
> > > > 2) issue an ECR / work with MS to make sure they understand the problem.
> > > >
> > > > This can be done in parallel. What I meant as a prerequisite is to start doing
> > > > 2) while we have 1) on table.
> > >
> > > Oh, okay, that makes sense. If you want to get (2) going, by all means
> > > go for it. I have no idea how to do this myself; Ard said something
> > > about joining the UEFI forum as an individual something or another but
> > > I don't think I'm the man for the job there. Is this something that
> > > Intel can do with their existing membership (is that the right term?)
> > > at the UEFI forum? Or maybe a Microsoft engineer on the list?
> >
> > My team at Microsoft, which works on Linux, filed a bug on this
> > issue against the Hyper-V team about a year ago, probably when the issue
> > was raised during the previous attempt to implement the functionality
> > in Linux.  I've talked with the Hyper-V dev manager, and they acknowledge
> > that the ACPI entry Hyper-V provides to guest VMs violates the spec.  But
> > changing to an identifier that meets the spec is problematic because
> > of backwards compatibility with Windows guests on Hyper-V that
> > consume the current identifier.  There's no practical way to have Hyper-V
> > provide a conformant identifier AND fix all the Windows guests out in
> > the wild to consume the new identifier.   As a result, at this point Hyper-V
> > is not planning to change anything.
> >
> > It's a lousy state-of-affairs, but as mentioned previously in this thread,
> > it seems to be one that we will have to live with.
> >
> 
> Thanks for chiming in.
> 
> Why not do something like
> 
> Name (_CID, Package (2) { "VM_GEN_COUNTER", "VMGENCTR" } )
> 
> ?
> 
> That way, older clients can match on the existing _CID and new clients
> can match on the spec compliant one.

I'll run this by the Hyper-V guys.  I don't have the ACPI expertise to disagree
with them when they say they can't change it. :-(

Michael