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

[Ian Campbell <Ian.Campbell@citrix.com>]

On Thu, 2014-11-06 at 17:01 -0500, Daniel De Graaf 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.

Can we take that as an ack?

Also needs the ok from Konrad as release manager. AIUI this is a bugfix
for a particular piece of h/w and as Daniel explains above the downside
is that sometimes someone might need to wait 0.75s for a timeout instead
of something shorter.