[SeaBIOS] Long delay: WARNING - Timeout at wait_reg8:81!

[Stephen Douthit]

On 03/07/2018 12:41 PM, Kevin O'Connor wrote:
> On Wed, Mar 07, 2018 at 12:33:36PM -0500, Stephen Douthit wrote:
>> On 03/07/2018 10:33 AM, Paul Menzel wrote:
>>> Dear Stephen,
>>>
>>>
>>> Thank you for your quick response.
>>>
>>> Am Dienstag, den 06.03.2018, 11:57 -0500 schrieb Stephen Douthit:
>>>> On 03/06/2018 11:04 AM, Paul Menzel wrote:
>>>>> On 03/02/18 17:31, Kevin O'Connor wrote:
>>>>>>
>>>>>> On Tue, Feb 27, 2018 at 02:17:08PM -0500, Stephen Douthit wrote:
>>>>> […]
>>>>>
>>>>>>
>>>>>> Thanks.  I committed this series.
>>>>> The second commit introduced a regression with coreboot on the
>>>>> ASRock E350M1. There are a bunch of time-outs, causing the startup
>>>>> to be really slow. With no serial console, the user thinks, it’s
>>>>> not working and start to debug.
>>>>
>>>> Looking through the the user manual for that board I don't see that it
>>>> has a TPM, or even the header for one, so a timeout seems correct.
>>>
>>> Indeed, no TPM is present.
>>
>> Thanks for confirming.
>>
>>>> Multiple 750ms timeouts does seem pretty painful though.  I hadn't
>>>> considered that tis_probe() would be called multiple times if no TPM
>>>> was present.
>>>>
>>>> What's the preferred way to have a probe function run and bail before
>>>> rerunning the timeout?  Just put a static flag in tis_probe()?  The
>>>> attached patch takes that approach.  Please let me know if that fixes
>>>> the issue for you, or if there's some other preferred pattern I should
>>>> use here.
>>>
>>> Unfortunately, that didn’t help.
>>>
>>> ```
>>> $ git log --oneline -2
>>> fd1cbb4 (HEAD -> master, origin/master, origin/HEAD) tpm: Save tis_probe() result to avoid a reun of lengthy timeouts
>>> 5adc8bd tpm: Handle unimplemented TIS_REG_IFACE_ID in tis_get_tpm_version()
>>> ```
>>>
>>> And the time-outs seem to be around 20 seconds or more. Please find the
>>> log with time stamps attached (`sudo ./readserial.py /dev/ttyUSB0`).
>>
>> Yikes, 20 seconds is the medium duration timeout, not the default A
>> timeout of 750ms.  I was poking the wrong area with the last patch.
>> It looks like tis_probe() is propagating the return from
>> tis_wait_access() in the no device present case.
> 
> FYI, even adding 5ms to the boot time is unacceptable.  Is there
> anyway to verify the hardware exists before waiting for it to be
> ready?

The only way I know of would be to check if we have TCPA or TPM2 ACPI
tables, and only attempt to probe for a TPM if those are present.

Attached patch should do that, and it's probably a good idea
independent of any of my other patches.
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