On 3/20/24 04:56, Jarkko Sakkinen wrote:
Based recent discussions on LKML, provide preliminary bits of tpm_tis_core
dependent drivers. Includes only bare essentials but can be extended later
on case by case. This way some people may even want to read it later on.
Cc: Jonathan Corbet <corbet@xxxxxxx>
CC: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Cc: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Peter Huewe <peterhuewe@xxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Alexander Steffen <Alexander.Steffen@xxxxxxxxxxxx>
Cc: keyrings@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-integrity@xxxxxxxxxxxxxxx
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
v2:
- Fixed errors reported by Randy:
https://lore.kernel.org/all/aed28265-d677-491a-a045-24b351854b24@xxxxxxxxxxxxx/
- Improved the text a bit to have a better presentation.
---
Documentation/security/tpm/index.rst | 1 +
Documentation/security/tpm/tpm_tis.rst | 30 ++++++++++++++++++++++++++
2 files changed, 31 insertions(+)
create mode 100644 Documentation/security/tpm/tpm_tis.rst
diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst
index fc40e9f23c85..f27a17f60a96 100644
--- a/Documentation/security/tpm/index.rst
+++ b/Documentation/security/tpm/index.rst
@@ -5,6 +5,7 @@ Trusted Platform Module documentation
.. toctree::
tpm_event_log
+ tpm_tis
tpm_vtpm_proxy
xen-tpmfront
tpm_ftpm_tee
diff --git a/Documentation/security/tpm/tpm_tis.rst b/Documentation/security/tpm/tpm_tis.rst
new file mode 100644
index 000000000000..b331813b3c45
--- /dev/null
+++ b/Documentation/security/tpm/tpm_tis.rst
@@ -0,0 +1,30 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+TPM FIFO interface Driver
+=========================
+
+FIFO (First-In-First-Out) is the name of the hardware interface used by the
FIFO is the type. I am surprised you call it a 'name'. I would say TIS
is the 'name'.
+tpm_tis_core dependent drivers. The prefix "tis" comes from the TPM Interface
tis is a tla -- a three letter *acronym*. You aren't using it as a 'prefix'.
+Specification, which is the hardware interface specification for TPM 1.x chips.
It's also available for TPM2.
+
+Communication is based on a 5 KiB buffer shared by the TPM chip through a
I thought it was typically 4 KiB.
+hardware bus or memory map, depending on the physical wiring. The buffer is
+further split into five equal-size buffers, which provide equivalent sets of
equal-sized MMIO regions?
+registers for communication between the CPU and TPM. These communication
+endpoints are called localities in the TCG terminology.
+
+When the kernel wants to send commands to the TPM chip, it first reserves
+locality 0 by setting the requestUse bit in the TPM_ACCESS register. The bit is
+cleared by the chip when the access is granted. Once it completes its
+communication, the kernel writes the TPM_ACCESS.activeLocality bit. This
+informs the chip that the locality has been relinquished.
+
+Pending localities are served in order by the chip in descending order, one at
+a time:
I think I know what pending localities are because I have worked with
this device but I am not sure whether the user can deduce this from the
paragraph above. Also, why this particular detail when the driver only
uses locality 0 and nobody is competing about access to localities?
+
+- Locality 0 has the lowest priority.
+- Locality 5 has the highest priority.
+
+Further information on the purpose and meaning of the localities can be found
+in section 3.2 of the TCG PC Client Platform TPM Profile Specification.
