Re: [Qemu-devel] [PATCH v3 3/4] acpi: build TPM Physical Presence interface

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 06/21/2018 09:21 AM, Marc-André Lureau wrote:
> Hi
>
> On Thu, Jun 21, 2018 at 2:54 PM, Igor Mammedov <imammedo@redhat.com> wrote:
>> On Tue, 15 May 2018 14:14:32 +0200
>> Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
>>
>>> From: Stefan Berger <stefanb@linux.vnet.ibm.com>
>>>
>>> The TPM Physical Presence interface consists of an ACPI part, a shared
>>> memory part, and code in the firmware. Users can send messages to the
>>> firmware by writing a code into the shared memory through invoking the
>>> ACPI code. When a reboot happens, the firmware looks for the code and
>>> acts on it by sending sequences of commands to the TPM.
>>>
>>> This patch adds the ACPI code. It is similar to the one in EDK2 but doesn't
>>> assume that SMIs are necessary to use. It uses a similar datastructure for
>>> the shared memory as EDK2 does so that EDK2 and SeaBIOS could both make use
>>> of it. I extended the shared memory data structure with an array of 256
>>> bytes, one for each code that could be implemented. The array contains
>>> flags describing the individual codes. This decouples the ACPI implementation
>>> from the firmware implementation.
>>>
>>> The underlying TCG specification is accessible from the following page.
>>>
>>> https://trustedcomputinggroup.org/tcg-physical-presence-interface-specification/
>>>
>>> This patch implements version 1.30.
>>>
>>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>>>
>>> ---
>>>
>>> v4 (Marc-André):
>>>   - replace 'DerefOf (FUNC [N])' with a function, to fix Windows ACPI
>>>      handling.
>>>   - replace 'return Package (..) {} ' with scoped variables, to fix
>>>     Windows ACPI handling.
>>>
>>> v3:
>>>   - add support for PPI to CRB
>>>   - split up OperationRegion TPPI into two parts, one containing
>>>     the registers (TPP1) and the other one the flags (TPP2); switched
>>>     the order of the flags versus registers in the code
>>>   - adapted ACPI code to small changes to the array of flags where
>>>     previous flag 0 was removed and now shifting right wasn't always
>>>     necessary anymore
>>>
>>> v2:
>>>   - get rid of FAIL variable; function 5 was using it and always
>>>     returns 0; the value is related to the ACPI function call not
>>>     a possible failure of the TPM function call.
>>>   - extend shared memory data structure with per-opcode entries
>>>     holding flags and use those flags to determine what to return
>>>     to caller
>>>   - implement interface version 1.3
>>> ---
>>>
>>>
>>  From ACPI pov I'd prefer PPI table documented somewhere in spec docs
>> (similar docs/specs/acpi_mem_hotplug.txt) and would look like in
>> other use-cases:
>>
>>     aml_append(field, aml_named_field("PPIN", 8)
>>
>> and drop "struct tpm_ppi" altogether replacing places it was used by
>> explicit constants.
> I have a slight preference for the tpm_ppi structure. But ok with
> replacing it with constant. Stefan, do you agree?

The PPI structure will appear in the firmware code and if it is the same 
and is correctly used we know that both are in sync. So I wouldn't get 
rid of it based on just that. If we have to changed all 
sizeof(uint32_t/uint8_t) to correctly use that shared structure, I'd 
prefer that.

     Stefan