Re: [PATCH] vTPM: Fix Atmel timeout bug.

[Emil Condrea <emilcondrea@gmail.com>]

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Daniel,
So, is the patch going to be approved(adjusting all short timeouts) or it
needs to be modified?

On Fri, Nov 7, 2014 at 12:01 AM, Daniel De Graaf <dgdegra@tycho.nsa.gov>
wrote:

> On 11/04/2014 05:15 AM, Ian Campbell wrote:
>
>> On Thu, 2014-10-30 at 15:48 +0200, Emil Condrea wrote:
>>
>>> Of course we can use max, but I thought that it might be useful to
>>> have a prink to inform the user that the timeout was adjusted.
>>> In init_tpm_tis the default timeouts are set using:
>>> /* Set default timeouts */ tpm->timeout_a =
>>> MILLISECS(TIS_SHORT_TIMEOUT);//750*1000000UL tpm->timeout_b =
>>> MILLISECS(TIS_LONG_TIMEOUT);//2000*1000000UL tpm->timeout_c =
>>> MILLISECS(TIS_SHORT_TIMEOUT); tpm->timeout_d =
>>> MILLISECS(TIS_SHORT_TIMEOUT);
>>>
>>>
>>>
>>> But in kernel fix they are set as 750*1000 instead of 750*1000000UL :
>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/
>>> linux.git/tree/drivers/char/tpm/tpm_tis.c#n381
>>> So if we want to integrate kernel changes I think we should use
>>> MICROSECS(TIS_SHORT_TIMEOUT) which is 750000
>>> Also in kernel the default timeouts are initialized using
>>> msecs_to_jiffies which is different from MILLISECS
>>> macro.: https://git.kernel.org/cgit/linux/kernel/git/torvalds/
>>> linux.git/tree/drivers/char/tpm/tpm_tis.c#n548
>>> Is there a certain reason for not using msecs_to_jiffies ?
>>>
>>
>> jiffies are a Linux specific concept which mini-os doesn't share.
>>
>> Daniel, do you have any opinion on this patch?
>>
>> It seems like the Linux fix is made only for the specifically broken
>> platform. That seems to make sense to me since presumably other systems
>> report short timeouts which they can indeed cope with. It's only Atmel
>> which brokenly reports something it cannot handle.
>>
>> Ian.
>>
>
> I agree that an adjustment is needed when values are too short.  Adjusting
> in all cases is not quite as nice as only fixing the broken TPMs, but it
> is a lot simpler.  It also doesn't seem harmful to have the timeouts be
> too large in the driver: a properly functioning TPM will not time out its
> requests in any case, so the user won't notice normally, and the default
> short timeout is 0.75 seconds - very few people will complain if they have
> to wait that long to get a timeout instead of what their TPM actually uses.
>
> --
> Daniel De Graaf
> National Security Agency
>

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