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

[Sasha Levin]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  .../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