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.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v4:
- Extended the text to address some of Stefan's concerns with v2.
- Had to unfortunately remove Randy's reviewed-by because of this, given
  the amount of text added.
v3:
- Fixed incorrect buffer size:
  https://lore.kernel.org/linux-integrity/d957dbd3-4975-48d7-abc5-1a01c0959ea3@linux.ibm.com/
v2:
- Fixed errors reported by Randy:
  https://lore.kernel.org/all/aed28265-d677-491a-a045-24b351854b24@infradead.org/
- Improved the text a bit to have a better presentation.
---
 Documentation/security/tpm/index.rst   |  1 +
 Documentation/security/tpm/tpm_tis.rst | 46 ++++++++++++++++++++++++++
 2 files changed, 47 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..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
+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/
-- 
2.44.0

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@gmail.com>

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

On Thu Apr 11, 2024 at 1:50 PM EEST, Bagas Sanjaya wrote:
> 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 ..."?

That would be better wording.

> > +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@gmail.com>


Thanks! I'll apply this with the fix you proposed.

For everyone: this is by no means perfect. The point is to seed
something we can build on top of. So I leave it rather lacking stuff
than try to document every possible bells and whistle. This can be
then improved based on discussions and future patch sets.

BR, Jarkko