Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 3

[Shannon Zhao <zhaoshenglong@xxxxxxxxxx>]

On 2015/8/18 16:15, Jan Beulich wrote:
>>>> On 18.08.15 at 09:35, <zhaoshenglong@xxxxxxxxxx> wrote:
>> Hi Jan,
>>
>> On 2015/8/18 13:14, Jan Beulich wrote:
>>>>>> Shannon Zhao <zhaoshenglong@xxxxxxxxxx> 08/18/15 5:46 AM >>>
>>>> On 2015/8/17 23:33, Jan Beulich wrote:
>>>>>>>> On 14.08.15 at 16:59, <shannon.zhao@xxxxxxxxxx> wrote:
>>>>>> 1. Copy and change some EFI and ACPI tables
>>>>>> -------------------------------------------
>>>>>
>>>>> While some explanation on the reasons for this was given in the past
>>>>> discussion, I'm still missing a word on the "why" for each of these here.
>>>>>
>>>>>> a) Copy EFI_SYSTEM_TABLE and change the value of FirmwareVendor,
>>>>>> VendorGuid, VendorTable, ConfigurationTable. These changes are not very
>>>>>> special and it just assign values to these members.
>>>>>
>>>>> I continue to question the need for fiddling with this table, not the
>>>>> least because I don't see how you intend to hand it to the Dom0
>>>>> kernel: Are you expecting to call the kernel's ordinary EFI entry
>>>>> point, despite it not itself running on EFI firmware?
>>>>>
>>>> Dom0 gets UEFI info from the minimal DT when booting with UEFI.
>>>> And the main purpose to create a EFI_SYSTEM_TABLE is to provide the ACPI
>>>> table root (RSDP) address to Dom0, so it could find the ACPI table.
>>>
>>> For that passing the configuration table would suffice. The more that Julien
>>> in his reply said you're not even intending to use the kernel's EFI stub. 
>> I.e.
>>> the question remains: How would you expect to hand the System Table
>>> pointer to Dom0?
>>>

The System Table pointer will be passed to Dom0 through the minimal DT
property "linux,uefi-system-table".

>>
>> Oh, I realize that there is some wrong expression about
>> EFI_SYSTEM_TABLE. We don't copy all the EFI System Table, but only the
>> EFI_SYSTEM_TABLE->Hdr. And assign the value of FirmwareVendor, set
>> NumberOfTableEntries to 1. Create only one EFI Configuration Table to
>> store Root table address. The other fields of EFI System Table stay
>> zero. So Dom0 only gets the ACPI table through System Table, others will
>> be invalid.
> 
> While this makes it look even more hacky, it doesn't answer the
> question.
> 
> Jan
> 
> 
> .
> 

-- 
Shannon


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