[PATCH v4 2/2] fTPM: add documentation for ftpm driver

[Sasha Levin]

This patch adds basic documentation to describe the new fTPM driver.

Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
Signed-off-by: Sasha Levin (Microsoft) <sashal@xxxxxxxxxx>
---
 Documentation/security/tpm/index.rst        |  1 +
 Documentation/security/tpm/tpm_ftpm_tee.rst | 31 +++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 Documentation/security/tpm/tpm_ftpm_tee.rst

diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst
index af77a7bbb0700..15783668644f2 100644
--- a/Documentation/security/tpm/index.rst
+++ b/Documentation/security/tpm/index.rst
@@ -4,4 +4,5 @@ Trusted Platform Module documentation
 
 .. toctree::
 
+   tpm_ftpm_tee
    tpm_vtpm_proxy
diff --git a/Documentation/security/tpm/tpm_ftpm_tee.rst b/Documentation/security/tpm/tpm_ftpm_tee.rst
new file mode 100644
index 0000000000000..29c2f8b5ed100
--- /dev/null
+++ b/Documentation/security/tpm/tpm_ftpm_tee.rst
@@ -0,0 +1,31 @@
+=============================================
+Firmware TPM Driver
+=============================================
+
+| Authors:
+| Thirupathaiah Annapureddy <thiruan@xxxxxxxxxxxxx>
+| Sasha Levin <sashal@xxxxxxxxxx>
+
+This document describes the firmware Trusted Platform Module (fTPM)
+device driver.
+
+Introduction
+============
+
+This driver is a shim for a firmware implemented in ARM's TrustZone
+environment. The driver allows programs to interact with the TPM in the same
+way the would interact with a hardware TPM.
+
+Design
+======
+
+The driver acts as a thin layer that passes commands to and from a TPM
+implemented in firmware. The driver itself doesn't contain much logic and is
+used more like a dumb pipe between firmware and kernel/userspace.
+
+The firmware itself is based on the following paper:
+https://www.microsoft.com/en-us/research/wp-content/uploads/2017/06/ftpm1.pdf
+
+When the driver is loaded it will expose ``/dev/tpmX`` character devices to
+userspace which will enable userspace to communicate with the firmware tpm
+through this device.
-- 
2.20.1