Re: [PATCH 2/2] reset: Add Infineon SLB9670 TPM reset driver

Francesco Dolcini
2023-12-18T17:35:08Z

Hello Lukas,

On Thu, Nov 23, 2023 at 09:59:43AM +0100, Lukas Wunner wrote:
> On Wed, Nov 22, 2023 at 04:15:18PM +0100, Francesco Dolcini wrote:
> > On Wed, Nov 22, 2023 at 12:29:49PM +0100, Lukas Wunner wrote:
> > > On Wed, Nov 22, 2023 at 12:33:58AM +0100, Francesco Dolcini wrote:
> > > > Not to mention that I was able to see the driver probe succeed in a
> > > > similar setup to the one you are describing in the commit message
> > > > (different board, arm64, but nothing done by the platform firmware).
> > >
> > > Hm, is the RST# pin even connected on that board?
> >
> > Yes, it's connected and it is asserted/de-asserted (aka toggled) during
> > startup from the HW reset circuit. However this is not implementing the
> > reset sequence you are implementing here.
>
> Section 4.5 of the datasheet seems to indicate that unless the sequence
> in Figure 3 is observed, the TPM may enter a defense mode against
> dictionary attacks "from which a recovery is very complex or even not
> possible."
>
> Simply toggling the RST# pin might therefore not be sufficient to ensure
> the TPM is operable.

I am trying to follow-up with infineon on this regard, do you already
have any insight from them maybe?

Maybe this procedure is relevant only when the device is in "security
defense state"?

Francesco