linux-kernel - Re: [PATCH 2/2] Documentation: tpm

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Date: Thu, 11 Apr 2024 17:50:09 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org
Cc: Alexander Steffen <Alexander.Steffen@...ineon.com>,
	"Daniel P . Smith" <dpsmith@...rtussolutions.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Jason Gunthorpe <jgg@...pe.ca>, Jonathan Corbet <corbet@....net>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	Mimi Zohar <zohar@...ux.ibm.com>, Peter Huewe <peterhuewe@....de>,
	Randy Dunlap <rdunlap@...radead.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Documentation: tpm_tis

On Tue, Apr 09, 2024 at 10:08:47PM +0300, Jarkko Sakkinen wrote:
> diff --git a/Documentation/security/tpm/tpm_tis.rst b/Documentation/security/tpm/tpm_tis.rst
> new file mode 100644
> index 000000000000..b448ea3db71d
> --- /dev/null
> +++ b/Documentation/security/tpm/tpm_tis.rst
> @@ -0,0 +1,46 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================
> +TPM FIFO interface driver
> +=========================
> +
> +TCG PTP Specification defines two interface types: FIFO and CRB. The former is
> +based on sequenced read and write operations,  and the latter is based on a
> +buffer containing the full command or response.
> +
> +FIFO (First-In-First-Out) interface is used by the tpm_tis_core dependent
> +drivers. Originally Linux had only a driver called tpm_tis, which covered
> +memory mapped (aka MMIO) interface but it was later on extended to cover other
> +physical interfaces supported by the TCG standard.
> +
> +For legacy compliance the original MMIO driver is called tpm_tis and the
Did you mean "For historical reasons above ..."?
> +framework for FIFO drivers is named as tpm_tis_core. The postfix "tis" in
> +tpm_tis comes from the TPM Interface Specification, which is the hardware
> +interface specification for TPM 1.x chips.
> +
> +Communication is based on a 20 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 4 KiB 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.
> +
> +References
> +==========
> +
> +TCG PC Client Platform TPM Profile (PTP) Specification
> +https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/

Other than that,

Reviewed-by: Bagas Sanjaya <bagasdotme@...il.com>

-- 
An old man doll... just what I always wanted! - Clara

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