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

[Lukas Wunner <lukas@wunner.de>]

Hi Francesco,

On Mon, Dec 18, 2023 at 06:34:00PM +0100, Francesco Dolcini wrote:
> 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"?

Sorry, I honestly don't know.  A colleague has talked to an FAE at an
Infineon reseller but they couldn't give a definitive answer either.
I'm very interested to hear whatever you learn from Infineon.

Thanks,

Lukas