[tbot] [PATCH] tbot: Provide login_delay parameter for Linux board

Lukasz Majewski lukma at denx.de
Tue Mar 5 10:11:08 UTC 2019

Hi Harald,

> Hello Lukasz,
> thank you for your patches!  The first one is perfect, I'll apply it
> asap. With the second one I'm not quite happy:  I tried to keep the
> use of timeouts to an absolute minimum in tbot to A) make it as fast
> as possible and B) as robust as possible. 

Those two are of course valid points. I don't want changing this as a
default behaviour - especially that those work perfectly on
boards which nicely just show login prompt after kernel start.

> Timeouts introduce
> unnecessary delays and can break easily if they were not set with
> enough tolerance (which makes things very sloow).

Yes, I'm aware of this.

However, there is a tradeoff:

The number of "adjustments" in tbot setup versus the number of changes
made to production setup (as changing root login to be password less,
changing the level of verbosity for console log).

The best would be to run production setup/device as is with tbot, but
this is very hard (like even when one has ssh keys for the production
device, the boot up info is not visible with ssh login, etc).

> Now I am completely aware of the issue you try to solve here as I
> have fought this exact problem myself in the past.  My current best
> bet for a solution would be calling `sysctl kernel.printk 1 1 1 1` at
> the start of each board session to at least keep the kernel from
> clobbering the console.

This is problematic as:

1. (I need to recheck this, but) - simple adding kernel printk level
for u-boot bootargs doesn't work (4 4 7 1) as it changes only to (1 4 7

2. As mentioned above - this alters the product in-field behaviour.

> But this is of course not implemented yet (mainly because of
> portability concerns) so I am willing to settle with your patch for
> now.

Please note, that it works only for password=None

> Thanks again!

Best regards,

Lukasz Majewski


DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma at denx.de
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