linux-kernel - Re: [PATCH v2 1/3] ftpm: dt-binding: add dts documentation for fTPM driver

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Date:   Wed, 10 Apr 2019 12:01:37 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        jgg@...pe.ca, Mark Rutland <mark.rutland@....com>,
        Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...rosoft.com,
        thiruan@...rosoft.com, bryankel@...rosoft.com
Subject: Re: [PATCH v2 1/3] ftpm: dt-binding: add dts documentation for fTPM driver

On Wed, Apr 10, 2019 at 11:19 AM Sasha Levin <sashal@...nel.org> wrote:
>
> On Tue, Apr 09, 2019 at 04:18:29PM -0500, Rob Herring wrote:
> >On Tue, Apr 9, 2019 at 1:50 PM Sasha Levin <sashal@...nel.org> wrote:
> >>
> >> The parameters are similar to the ones used by IBM's vTPM and the
> >> various I2C tpm drivers.
> >
> >Bindings describe h/w (or firmware interfaces in this case), not drivers.
> >
> >>
> >> Signed-off-by: Sasha Levin <sashal@...nel.org>
> >> ---
> >>  .../bindings/security/tpm/tpm_ftpm_tee.txt          | 13 +++++++++++++
> >>  .../devicetree/bindings/vendor-prefixes.txt         |  1 +
> >>  2 files changed, 14 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/security/tpm/tpm_ftpm_tee.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/security/tpm/tpm_ftpm_tee.txt b/Documentation/devicetree/bindings/security/tpm/tpm_ftpm_tee.txt
> >> new file mode 100644
> >> index 000000000000..20fca67a56c4
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/security/tpm/tpm_ftpm_tee.txt
> >> @@ -0,0 +1,13 @@
> >> +Required properties:
> >> +- compatible: should be "microsoft,ftpm"
> >> +- linux,sml-base: 64-bit base address of the reserved memory allocated
> >> +                 for the firmware event log
> >> +- linux,sml-size: size of the memory allocated for the firmware event log
> >
> >Firmware is defining linux specific properties? What if I want to run
> >BSD? We should use 'reg' here instead.
>
> This is based on already existing code that defines these names, see
> tpm_read_log_of() in drivers/char/tpm/eventlog/of.c .

BTW, that probably needs updating to handle endianness correctly.

> These properties were described similarily by other interfaces (see
> Documentation/devicetree/bindings/security/tpm/ibmvtpm.txt or
> Documentation/devicetree/bindings/security/tpm/tpm-i2c.txt for example).
>
> We could rename them all if you'd like, I was just trying to follow the
> existing code.
>
> >What memory is used here? This should be under /reserved-memory if it
> >is part of "main" memory.
>
> That's my understanding, yes.
>
> >Really, I'd prefer to not see this in DT at all. Make the firmware
> >discoverable. Why repeat the mistakes of non-discoverable h/w in s/w
> >interfaces? OP-Tee at least has defined a mechanism to enumerate TEE
> >functions IIRC.
>
> Sadly the firmware already exists as-is on live hardware, there is a
> paper describing it back from 2016 and we're stuck having to support
> that.

Does the firmware depend on this binding or the DT just gets
statically populated with the address/size the firmware hardcodes? I'd
prefer not to propagate the IBM binding that we were kind of stuck
with. I had similar comments on it...

Are there other parts of the TEE firmware that need to be described in DT?

Rob