Re: [PATCH] Documentation: tpm_tis

["Jarkko Sakkinen" <jarkko@kernel.org>]

Some remarks below that I noticed after sending this.

On Mon Mar 4, 2024 at 11:27 PM EET, Jarkko Sakkinen wrote:
> Based recent discussions on LKML, provide preliminary bits of tpm_tis_core

s/Based/ Based on/

> 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@lwn.net>
> CC: Daniel P. Smith <dpsmith@apertussolutions.com>
> Cc: Lino Sanfilippo <l.sanfilippo@kunbus.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Peter Huewe <peterhuewe@gmx.de>
> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
> Cc: Alexander Steffen <Alexander.Steffen@infineon.com>
> Cc: keyrings@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-integrity@vger.kernel.org
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
>  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..3cec0216a169
> --- /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
> +`tpm_tis_core` dependent drivers. The prefix "tis" is named after TPM
> +Interface Specification, which is the hardware interface specification for
> +TPM 1.x chips.
> +
> +Communication is based on a 5 KiB buffer shared by the TPM chip through a
> +hardware bus or memory map. The buffer is further split to five equal size

s/to/into/

> +buffers, which provide equivalent sets of registers for communication
> +between CPU and TPM. The communication end points are called *localities*
> +in the TCG terminology.
> +
> +When a kernel wants to send a commands to the TPM chip, it first reserves

s/a kernel/kernel/
s/a commands/commands/
> +locality 0 by setting `requestUse` bit in `TPM_ACCESS` register. The bit is
> +cleared by the chip when the access is granted. Once completed its
> +communication, it sets `activeLocity` bit in the same register.

s/it sets/kernel relinquishes reservation by setting/

> +
> +Pending localities are served in order by the chip descending orderm and
> +one at a time:

"Pending localities are served in descending order and one at a time:"

> +
> +- Locality 0 has the lowest priority.
> +- Locality 5 has the highest priotiy.
> +
> +Further information on purpose and meaning of the localities can be found
> +from section 3.2 of TCG PC Client Platform TPM Profile Specification.

s/on purpose/on the purpose/

BR, Jarkko