On 06/19/2018 06:10 AM, Jarkko Sakkinen wrote:

On Tue, Jun 12, 2018 at 10:58:26AM -0700, Tadeusz Struk wrote:

quoted

The TCG SAPI specification [1] defines a set of functions, which allows
applications to use the TPM device in either blocking or non-blocking fashion.
Each command defined by the specification has a corresponding
Tss2_Sys_<COMMAND>_Prepare() and Tss2_Sys_<COMMAND>_Complete() call, which
together with Tss2_Sys_ExecuteAsync() is designed to allow asynchronous
mode of operation. Currently the TPM driver supports only blocking calls,
which doesn't allow asynchronous IO operations.
This patch changes it and adds support for nonblocking write and a new poll
function to enable applications, which want to take advantage of this feature.
The new functionality can be tested using standard TPM tools implemented
in [2], together with modified TCTI from [3].

[1] https://trustedcomputinggroup.org/wp-content/uploads/TSS_SAPI_Version-1.1_Revision-22_review_030918.pdf
[2] https://github.com/tpm2-software/tpm2-tools
[3] https://github.com/tstruk/tpm2-tss/tree/async

For me the value is still a bit questionable. The benchmark looks a bit
flakky to give much figures how this would work with real world workloads.

I read James response and I also have to question why not just a worker
thread in user space? TPM does only one command at a time anyways.

Cannot take this in before I know that user space will (1) adapt to
this and (2) gain value compared to a worker thread.

Hi Jarkko,
Thanks for reviewing the patch.
There are applications/frameworks where a worker thread is not an option.
Take for example the IoT use-cases and frameworks like IoT.js, or "Node.js for IoT".
They are all single threaded, event-driven frameworks, using non-blocking I/O as the base of their processing model.
Similarly embedded applications, which are basically just a single threaded event loop, quite often don't use threads because of resources constrains.

If your concern is that user space will not adopt to this, I can say that TSS library [1] is currently blocked on this feature, and we can not enable some of the use-cases mentioned above because of this.

Thanks,
Tadeusz

[1] https://github.com/tpm2-software/tpm2-tss
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