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

From: Javier Martinez Canillas
Date: Wed Dec 20 2017 - 10:31:24 EST

Hello Azhar,

On 12/20/2017 04:08 PM, Shaikh, Azhar wrote:


>>>> 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 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.

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