Documentation/security/tpm/tpm_tis.rst - linux - Git at Google

 .. 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 historical reasons above the original MMIO driver is called tpm_tis and the
 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/
	.. 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 historical reasons above the original MMIO driver is called tpm_tis and the
	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/