Am 13. September 2017 11:52:12 GMT-07:00 schrieb Ken Goldman [off-list ref]:

On 9/6/2017 12:12 PM, Jason Gunthorpe wrote:

quoted

The problem with this approach is that the TPM could totally block
the CPU for very long periods of time.

It seems very risky to enable..

How would you characterize "very long"?

The TPM vendors confirm that they empty the FIFO at internal speeds
that
are comparable to the bus speed.  Thus, any stall will be sub-usec.  Is
that an issue?

If the tpm does behave correctly, this is fine. 
If the tpm hangs for whatever reason, your machine is frozen and you will never figure out why.

That's my concern there.
However ddwg seems fine.

In addition, new TPMs have ever larger FIFO's, making stalls less
likely
going forward.

But also reduced the polling loops that introduce the performance penalty ;)

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