Re: [Xen-devel] [PATCH v4 1/2] tools/libacpi: update FADT layout to support version 5

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Tue, Dec 13, 2016 at 02:03:06AM -0700, Jan Beulich wrote:
> >>> On 12.12.16 at 17:04, <roger.pau@xxxxxxxxxx> wrote:
> > Update the structure of the FADT table to version 5, and use that version 
> > for
> > PVHv2 guests. Note that HVM guests will continue to use FADT 4. In order to 
> > do
> > this, add a new field to acpi_config that contains the ACPI revision to use 
> > by
> > libacpi. Note that currently this only applies to the FADT.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> To be honest I'm of two minds here. On one hand the patch is fine
> as is for the immediate purpose. On the other hand I would have
> hoped for a little more complete handling of this:
> - The spec is at version 6.1 - I don't see why we should give anything
>   less to PVHv2 guests, causing possible compatibility issues going
>   forward.

I'm not opposed to bumping the ACPI version to 6.1, it's just that this needs 
to 
be properly done IMHO, and I would like to see all tables bumped to the 
revision 
specified in 6.1. This is the minor bump needed in order to use the no RTC 
flag, 
so I feel it's safer, and other tables should not get that much off-sync 
compared to FADT.

> - The version consists of both a major and a minor part, yet no
>   provisions are being made to allow for this.

Given the nature of this "fix" (which initially only focused on being able to 
use the no RTC flag) I didn't see the need to introduce the minor version. TBH, 
the FADT field used for the minor version is still marked as "reserved" in our 
current layout. I would prefer that to be done in a proper patch series that 
fixes all this minor issues and properly bumps the version to 6.1.

Roger.

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