Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount

Michal Suchánek
2017-08-16T10:24:27Z

On Tue, 15 Aug 2017 18:02:57 -0400
Ken Goldman <kgold@linux.vnet.ibm.com> wrote:

> On 8/13/2017 7:53 PM, msuchanek wrote:
> > About 500 out of 700 mainboards sold today has a PS/2 port which is
> > probably due to prevalence of legacy devices and usbhid limitations.
> >
> > Similarily many boards have serial and parallel hardware ports.
> >
> > In all diagrams detailed enough to show these ports I have seen them
> > attached to the LPC bus.
>
> Do these boards have a TPM? Remember that the TPM requires special
> LPC bus cycles.

Out of nearly 700 boards over 500 have PS/2 connector and over 400
have TPM slot (which is subset of the PS/2 enabled boards). Some more
possibly have on-board TPM chip.

>
> Even if so, the TPM LPC bus wait states are less than a usec. My
> thought is that it's unlikely that any device (serial port, mouse,
> keyboard, printer) will be adversely affected.

Yes, in theory this is negligible. So unless there is a possibility
these wait states chain or the device otherwise takes over the bus for
extended period of time this should be fine.

Thanks

Michal