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

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Message-Id: <CZLFVTVPBFB4.3IIZULN3LKZGI@kernel.org>
Date: Tue, 05 Mar 2024 03:52:41 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Randy Dunlap" <rdunlap@...radead.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 Tue Mar 5, 2024 at 12:53 AM EET, Randy Dunlap wrote:
>
>
> 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 ?

Yes.

>
> > +
> > +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.

Thanks for the remarks. Too many typos but at least I think the story is
is understandable and describes pretty well key elements of tpm_tis_core.

BR, Jarkko