Re: [Xen-devel] [PATCH] vTPM: Fix Atmel timeout bug.

[Emil Condrea <emilcondrea@xxxxxxxxx>]

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@xxxxxxxxxxxxx> 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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