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

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  Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance  by ignoring burstcount msuchanek <msuchanek@suse.de> - 2017-08-14 02:00 +0200
    Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance by  ignoring burstcount Ken Goldman <kgold@linux.vnet.ibm.com> - 2017-08-16 00:10 +0200
      Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance  by ignoring burstcount Michal Suchánek <msuchanek@suse.de> - 2017-08-16 12:30 +0200

#1710591 — Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount

Hello,

On Fri, 11 Aug 2017 17:32:12 -0400
Ken Goldman <kgold@linux.vnet.ibm.com> wrote:

> On 8/9/2017 5:00 PM, Peter Huewe wrote:
> > 
> > Since we are the linux kernel, we do have to care for legacy
> > devices. And a system with LPC, PS2Mouse on SuperIO and a TPM are
> > not that uncommon.
> > 
> > And heck, we even have support for 1.1b TPM devices....  
> 
> Understood.  However, remember that SuperIO is a 1980's device that
> predates the TPM.  Since the TPM requires special LPC bus cycles, it's
> even less likely that an old chipset has an attached TPM.

Where are the PS/2 ports attached today? 

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.

Thanks

Michal

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#1712495 — Re: [tpmdd-devel] [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount

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.

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.

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#1712825

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

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