RE: [PATCH 0/4] tpm: fix PS/2 devices not working on Braswell systems due CLKRUN enabled

Shaikh, Azhar
2017-12-20T15:42:07Z

>-----Original Message-----
>From: Javier Martinez Canillas [mailto:javierm@redhat.com]
>Sent: Wednesday, December 20, 2017 7:31 AM
>To: Shaikh, Azhar <azhar.shaikh@intel.com>;
>Alexander.Steffen@infineon.com; hdegoede@redhat.com; linux-
>kernel@vger.kernel.org
>Cc: james@ettle.org.uk; arnd@arndb.de; jarkko.sakkinen@linux.intel.com;
>peterhuewe@gmx.de; jgg@ziepe.ca; gregkh@linuxfoundation.org; linux-
>integrity@vger.kernel.org
>Subject: Re: [PATCH 0/4] tpm: fix PS/2 devices not working on Braswell
>systems due CLKRUN enabled
>
>Hello Azhar,
>
>On 12/20/2017 04:08 PM, Shaikh, Azhar wrote:
>
>[snip]
>
>>>>
>>>>> It seems that on machines with a PS/2 controller connected to the
>>>>> LPC bus the BIOS is already doing this, so I've a feeling that it
>>>>> not being done on devices with a TPM is a bug in the firmware
>>>>
>>>> Absolutely agree, system integratos should make sure that all the
>>>> devices connected to the LPC either have CLKRUN protocol support and
>>>> is enabled or disable the CLKRUN protocol permanently.
>>>
>>> As far as I understand it, this is exactly the issue here: They know
>>> that there are devices that do not support the CLKRUN protocol (the
>>> TPM in this case), but they still need to enable it to prevent other
>>> issues. So for the TPM to continue to work, CLKRUN needs to be
>>> disabled temporarily while the TPM is active.
>>>
>>
>> Yes that was the reason to have this fix. We needed CLKRUN to be enabled
>for Braswell SOC . But the TPM in this case SLB9655 does not support CLKRUN
>(please check this public documentation
>https://www.infineon.com/dgdl/Infineon-TPM+SLB+9665-DS-v10_15-
>EN.pdf?fileId=5546d4625185e0e201518b83d9273d87 section 2.3 Power
>Management). So as Alexander mentioned CLKRUN is disabled while TPM
>transactions are in progress.
>>
>
>Yes I do understand that. Please read my answer to Alexander's email and
>also my question (and Hans') about keeping the CLKRUN protocol
>permanently disabled.
>

We had to enable CLKRUN for BSW issues as mentioned here https://www.intel.com/content/www/us/en/processors/pentium/pentium-celeron-n-series-spec-update.html on Page 24 CHP 49 and Page 25 CHP 51

>Best regards,
>--
>Javier Martinez Canillas
>Software Engineer - Desktop Hardware Enablement Red Hat