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

[Laszlo Ersek <lersek@redhat.com>]

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