Re: [PATCH v2] tpm: use a map for tpm2_calc_ordinal_duration()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Sep 18, 2025 at 10:49:28PM -0500, Serge E. Hallyn wrote:
> On Thu, Sep 18, 2025 at 10:30:18PM +0300, Jarkko Sakkinen wrote:
> > The current shenanigans for duration calculation introduce too much
> > complexity for a trivial problem, and further the code is hard to patch and
> > maintain.
> > 
> > Address these issues with a flat look-up table, which is easy to understand
> > and patch. If leaf driver specific patching is required in future, it is
> > easy enough to make a copy of this table during driver initialization and
> > add the chip parameter back.
> > 
> > 'chip->duration' is retained for TPM 1.x.
> > 
> > As the first entry for this new behavior address TCG spec update mentioned
> > in this issue:
> > 
> > https://github.com/raspberrypi/linux/issues/7054
> > 
> > Therefore, for TPM_SelfTest the duration is set to 3000 ms.
> > 
> > This does not categorize a as bug, given that this is introduced to the
> > spec after the feature was originally made.
> > 
> > Cc: Frédéric Jouen <fjouen@sealsq.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> 
> fwiw (which shouldn't be much) looks good to me, but two questions,
> one here and one below.
> 
> First, it looks like in the existing code it is possible for a tpm2
> chip to set its own timeouts and then set the TPM_CHIP_FLAG_HAVE_TIMEOUTS
> flag to avoid using the defaults, but I don't see anything using that
> in-tree.  Is it possible that there are out of tree drivers that will be
> sabotaged here?  Or am I misunderstanding that completely?

Good questions, and I can brief a bit about the context of the
pre-existing art and this change.

This complexity was formed in 2014 when I originally developed TPM2
support and the only available testing plaform was early Intel PTT with
a flakky version of TPM2 support (e.g., no localities).

Since then we haven't had per leaf-driver divergence.

Further, I think that this type of layout is actually a  better fit if
we ever need to quirks for command durations for a particular device, as
then we can migrate to "copy and patch" semantics i.e., have a copy of
this map in the chip structure.

As per out-of-tree drivers, it's unfortunate reality of out-of-tree
drivers :-) However, this will definitely add some extra work, when
backporting fixes (not overwhelmingly much).

BR, Jarkko