Re: [PATCH v2] Documentation: tpm_tis

[Randy Dunlap]

Hi,

On 3/20/24 01:56, 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>

Makes sense to me. Thanks.

Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

> ---
> 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
> +tpm_tis_core dependent drivers. The prefix "tis" comes from the 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, depending on the physical wiring. The buffer is
> +further split into five equal-size buffers, which provide equivalent sets of
> +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:
> +
> +- 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.

-- 
#Randy