[PATCH v3 1/3] docs/specs/tpm: document PPI support on ARM64 virt

[Mohammadfaiz Bawa <mbawa@redhat.com>]

Document that tpm-tis-device on the ARM virt machine supports PPI
with dynamically allocated MMIO via the platform bus, unlike x86
where PPI is at the fixed address 0xFED45000.

Also add hw/arm/virt-acpi-build.c and hw/acpi/tpm.c to the list
of files related to TPM ACPI tables.

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mohammadfaiz Bawa <mbawa@redhat.com>
---
 docs/specs/tpm.rst | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/docs/specs/tpm.rst b/docs/specs/tpm.rst
index b630a351b4..ba2b0d7267 100644
--- a/docs/specs/tpm.rst
+++ b/docs/specs/tpm.rst
@@ -187,8 +187,32 @@ The location of the table is given by the fw_cfg ``tpmppi_address``
 field.  The PPI memory region size is 0x400 (``TPM_PPI_ADDR_SIZE``) to
 leave enough room for future updates.
 
+PPI on ARM64 virt
+-----------------
+
+The ARM virt machine supports PPI for ``tpm-tis-device`` as defined
+in the `PPI specification`_.
+
+Unlike the x86 TIS device where the PPI memory region is mapped at
+the fixed address ``0xFED45000`` (within the TIS MMIO range), the
+ARM64 sysbus device registers PPI memory as a second MMIO region
+on the platform bus. The platform bus assigns the guest physical
+address dynamically at device plug time. The ACPI ``_DSM`` method
+and PPI operation regions reference this dynamically resolved
+address.
+
+PPI is controlled by the ``ppi`` property (default ``on``)::
+
+    -device tpm-tis-device,tpmdev=tpm0,ppi=on
+
+Without PPI, guest operating systems such as Windows 11
+ARM64 will log errors when attempting to query TPM Physical
+Presence capabilities via the ACPI ``_DSM`` method.
+
 QEMU files related to TPM ACPI tables:
  - ``hw/i386/acpi-build.c``
+ - ``hw/arm/virt-acpi-build.c``
+ - ``hw/acpi/tpm.c``
  - ``include/hw/acpi/tpm.h``
 
 TPM backend devices
-- 
2.53.0