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