Re: [Qemu-devel] [PATCH RFC] acpi: add reset register to fadt

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 01, 2017 at 05:03:38PM +0100, Laszlo Ersek wrote:
> On 02/01/17 16:16, Igor Mammedov wrote:
> > On Wed, 1 Feb 2017 14:03:52 +0100
> > Laszlo Ersek <lersek@redhat.com> wrote:
> > 
> >> On 02/01/17 13:52, Laszlo Ersek wrote:
> >>> On 02/01/17 12:37, Igor Mammedov wrote:  
> >>>> On Tue, 31 Jan 2017 20:17:02 +0200
> >>>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >>>>  
> >>>>> On Tue, Jan 31, 2017 at 05:28:57PM +0100, Laszlo Ersek wrote:  
> >>>>>> The ACPI 6.1 spec says,
> >>>>>>
> >>>>>> - DSDT: [...] If the X_DSDT field contains a non-zero value then this
> >>>>>>   field must be zero.
> >>>>>> - X_DSDT: [...] If the DSDT field contains a non-zero value then this
> >>>>>>   field must be zero.    
> >>>>>
> >>>>> But that's only 6.1. 6.0 and earlier did not say this.
> >>>>> The errata they wanted to address was:
> >>>>> 1393 In FADT: if X_DSDT field is non-zero, DSDT
> >>>>> field should be ignored or deprecated
> >>>>>
> >>>>> I would class this as a spec bug.
> >>>>>  
> >>>>
> >>>> The same applies to X_PM1a_EVT_BLK and co,
> >>>> for example 5.1 spec "This is a required
> >>>> field."
> >>>>
> >>>> And looks like Windows implemented it as mandatory
> >>>> to boot perhaps to be compatible with 5.1 and earlier
> >>>> specs.
> >>>>
> >>>> It appears fw would be forced to fill fields depending
> >>>> on table revision.  
> >>>
> >>> Sounds like a valid point.
> >>>
> >>> I compared the FADT defintion between ACPI 5.1 and ACPI 6.1. Indeed, the
> >>> former says:
> >>>
> >>> - FADT Major Version: 5; Major Version of this FADT structure, [...]
> >>> - DSDT: Physical memory address (0-4 GB) of the DSDT.
> >>> - X_DSDT: 64bit physical address of the DSDT.
> >>>
> >>> the latter says:
> >>>
> >>> - FADT Major Version: 6; Major Version of this FADT structure, [...]
> >>>
> >>> - DSDT: Physical memory address of the DSDT. If the X_DSDT field
> >>>   contains a non-zero value then this field must be zero.
> >>>
> >>> - X_DSDT: Extended physical address of the DSDT. If the DSDT field
> >>>   contains a non-zero value then this field must be zero.
> >>>
> >>> I will ask on edk2-devel whether the
> >>> "MdeModulePkg/Universal/Acpi/AcpiTableDxe" maintainers can think of a
> >>> way to accommodate this.  
> >>
> >> Sigh, this looks nasty.
> >>
> >> Considering specifically the DSDT <-> X_DSDT question, Mantis ticket
> >> #1393 (which requires the mutual exclusion) went into 5.1B. In version
> >> 5.1A, the mutual exclusion is not required.
> >>
> >> Unfortuantely, the FADT Major.Minor version, as reported through the
> >> bytes at offsets 8 and 131 decimal in the table, is "5.1" for *both*
> >> 5.1A and 5.1B. In other words, looking at just Major.Minor, it cannot be
> >> determined with full precision whether the DSDT and X_DSDT fields should
> >> be exclusive or not. :/
> > The same applies to 6.0 vs 6.0A 
> 
> Thanks for the info; I've updated the patch!
> 
> Laszlo

Same applies for firmware control. There, the difference would be
between 3.0 and 4.0 where they made the incompatible change.

-- 
MST