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SubjectRE: [PATCH v4 4/7] tpm: tpm_tis: Fix expected bit handling and send all bytes in one shot without last byte in exception
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> On Tue, Mar 31, 2020 at 02:32:04PM +0300, amirmizi6@gmail.com wrote:
> > From: Amir Mizinski <amirmizi6@gmail.com>
> >
> > Today, actual implementation for send massage is not correct. We check
> > and loop only on TPM_STS.stsValid bit and next we single check
> > TPM_STS.expect bit value.
> > TPM_STS.expected bit shall be checked in the same time of
> > TPM_STS.stsValid, and should be repeated until timeout_A.
> > To aquire that, "wait_for_tpm_stat" function is modified to
> > "wait_for_tpm_stat_result". this function read regulary status
> > register and check bit defined by "mask" to reach value defined in "mask_result"
> > (that way a bit in mask can be checked if reached 1 or 0).
> >
> > Respectively, to send message as defined in
> > TCG_DesignPrinciples_TPM2p0Driver_vp24_pubrev.pdf, all bytes should be
> > sent in one shot instead of sending last byte in exception.
> >
> > This improvment was suggested by Benoit Houyere.

>Use suggested-by tag.

>Also if something is not correct, please provide a fixes tag.

> You are speaking now in theoretical level, which we don't really care that much. Is this causing you real issues? If the answer is yes, please report them. If the > >answer is no, we don't need this.

> /Jarkko

I2C TPM specification introduce CRC calculation on TPM command bytes. CRC calculation take place from last byte acquired to TPM_STS.expected bit reset (=0) .It introduces latency and actual incorrect implementation becomes visible now under I2C on the contrary before that's all.
The case where TPM keeps TPM_STS.expected bit set with TPM_STS.stsValid set after last byte reception is possible and is not an issue. It's not theoretical level, it's practical level now.


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