[PATCH v3 1/3] docs: Add support for TPM devices over I2C bus

[Ninad Palsule]

This is a documentation change for I2C TPM device support.

Qemu already supports devices attached to ISA and sysbus.
This drop adds support for the I2C bus attached TPM devices.

Signed-off-by: Ninad Palsule <ninad@linux.ibm.com>

---
V2:

Incorporated Stephen's review comments
- Added example in the document.
---
 docs/specs/tpm.rst | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/docs/specs/tpm.rst b/docs/specs/tpm.rst
index 535912a92b..bf7249b09c 100644
--- a/docs/specs/tpm.rst
+++ b/docs/specs/tpm.rst
@@ -21,11 +21,15 @@ QEMU files related to TPM TIS interface:
  - ``hw/tpm/tpm_tis_common.c``
  - ``hw/tpm/tpm_tis_isa.c``
  - ``hw/tpm/tpm_tis_sysbus.c``
+ - ``hw/tpm/tpm_tis_i2c.c``
  - ``hw/tpm/tpm_tis.h``
 
 Both an ISA device and a sysbus device are available. The former is
 used with pc/q35 machine while the latter can be instantiated in the
-Arm virt machine.
+Arm virt machine. An I2C device support is also added which can be
+instantiated in the arm based emulation machine. An I2C device is also
+supported for the Arm virt machine. This device only supports the
+TPM 2 protocol.
 
 CRB interface
 -------------
@@ -348,6 +352,20 @@ In case an Arm virt machine is emulated, use the following 
command line:
     -drive if=pflash,format=raw,file=flash0.img,readonly=on \
     -drive if=pflash,format=raw,file=flash1.img
 
+In case a Rainier bmc machine is emulated, use the following command line:
+
+.. code-block:: console
+
+  qemu-system-arm -M rainier-bmc -nographic \
+    -kernel ${IMAGEPATH}/fitImage-linux.bin \
+    -dtb ${IMAGEPATH}/aspeed-bmc-ibm-rainier.dtb \
+    -initrd ${IMAGEPATH}/obmc-phosphor-initramfs.rootfs.cpio.xz \
+    -drive 
file=${IMAGEPATH}/obmc-phosphor-image.rootfs.wic.qcow2,if=sd,index=2\
+    -net nic -net 
user,hostfwd=:127.0.0.1:2222-:22,hostfwd=:127.0.0.1:2443-:443\
+    -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \
+    -tpmdev emulator,id=tpm0,chardev=chrtpm \
+    -device tpm-tis-i2c,tpmdev=tpm0,bus=aspeed.i2c.bus.12,address=0x2e
+
 In case SeaBIOS is used as firmware, it should show the TPM menu item
 after entering the menu with 'ESC'.
 
-- 
2.37.2