Re: [GIT PULL] TPM DEVICE DRIVER: tpmdd-next-v6.18-2

Jarkko Sakkinen
2025-10-10T17:26:42Z

On Fri, Oct 10, 2025 at 08:51:09AM -0700, Linus Torvalds wrote:
> On Thu, 9 Oct 2025 at 22:35, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git tags/tpmdd-next-v6.18-2
>
> So I've pulled this, but I'm still unhappy about the explanation.
>
> You tried to explain a one-line single-character change in that pull
> request, and even in that explanation you spent most effort on
> dismissing other peoples concerns.

For what it is, most of it comes from:

1. "tpm: use a map for tpm2_calc_ordinal_duration()"
Flattened out timeout calculations to a table and increase timeout
for TPM2_SelfTest, which addresses longer timeout on Raspeberry Pi.
2. "tpm: Prevent local DOS via tpm/tpm0/ppi/*operations"
Caches TPM physical presence interface ACPI functions on first run
instead of requesting for every read.

Also:

1. I went through Chris' email because you asked to refer to it.
2. I also spent time re-testing O_EXCL change throughly once more. From
my subjective perspective I was exactly trying to address other people's
concerns.

That said, I fell off the track and yeah not well delivered agreed.

> That one-liner would have been - and is - sufficiently explained by
> "it performs badly and breaks some configurations". There's absolutely
> no reason to then go on to describe how *you* don't care about those
> configurations.

Maybe I had a bad choice of words but there's no configuration that
breaks with anything sold as discrete TPM chips, embedded SoC, fTPM's
or anything really. I got the impression of a bug in the wild, other
than the perf regression.

>
> But lookie here:
>
> 8 files changed, 137 insertions(+), 199 deletions(-)
>
> that's the actual meat of the pull request, and it gets not a peep of
> commentary.
>
> I'd also like to point out that Microsoft spent *years* trying to do
> the "we require certain typical TPM setups", and people complained
> about their idiocy.
>
> For all I know, they still push that crap.
>
> I would certainly are *NOT* that stupid, and we are not going down that path.
>
> So when it comes to TPM, the rule is not "typical cases work".
>
> The rule is "if it causes problems, we acknowledge them and we avoid them".

I deeply care anything that can be bought with money or even anything
that drifts away from a spec manageable amount.

> Thus the whole "disable TCG_TPM2_HMAC" really doesn't merit this kind
> of long explanation.
>
> In contrast, the *other* changes are probably much more interesting than that.

Very true :-)

> Linus

BR, Jarkko