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 12:19:49 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Rob Herring <robh+dt@...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 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 .

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.

--
Thanks,
Sasha