linux-kernel - Re: [PATCH] Documentation: tpm

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Message-ID: <aed28265-d677-491a-a045-24b351854b24@infradead.org>
Date: Mon, 4 Mar 2024 14:53:11 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-doc@...r.kernel.org
Cc: Jonathan Corbet <corbet@....net>,
 "Daniel P . Smith" <dpsmith@...rtussolutions.com>,
 Lino Sanfilippo <l.sanfilippo@...bus.com>, Jason Gunthorpe <jgg@...pe.ca>,
 Peter Huewe <peterhuewe@....de>,
 James Bottomley <James.Bottomley@...senPartnership.com>,
 Alexander Steffen <Alexander.Steffen@...ineon.com>,
 keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-integrity@...r.kernel.org
Subject: Re: [PATCH] Documentation: tpm_tis



On 3/4/24 13:27, 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@....net>
> CC: Daniel P. Smith <dpsmith@...rtussolutions.com>
> Cc: Lino Sanfilippo <l.sanfilippo@...bus.com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Peter Huewe <peterhuewe@....de>
> Cc: James Bottomley <James.Bottomley@...senPartnership.com>
> Cc: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Cc: keyrings@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-integrity@...r.kernel.org
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.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/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
> +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
> +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.

      Is that              activeLocality ?

> +
> +Pending localities are served in order by the chip descending orderm and
> +one at a time:
> +
> +- Locality 0 has the lowest priority.
> +- Locality 5 has the highest priotiy.

                                priority.

> +
> +Further information on purpose and meaning of the localities can be found
> +from section 3.2 of TCG PC Client Platform TPM Profile Specification.

-- 
#Randy