[coreboot] locking...

Stefan Reinauer stepan at coresystems.de
Fri Jun 19 19:41:18 CEST 2009

Carl-Daniel Hailfinger wrote:
>> I never got this done, I only got the "AP post code"
>> working. But overall I think my SMP startup prototype was much cleaner
>> than what is in v2 today.
> I don't understand v2 startup anyway (well, except for your new code).

Then please go ahead and learn to read it... It's important that we
understand what's going on before changing it.

The new code just duplicates what was there, but it adds a couple of new
breakages. It doesn't even add any conceptional differences.

>> I don't think we want to put locks in printk. If an AP gets part way
>> up, takes the lock, and fails, everyone is going to stick on that
>> lock. Not fun.
> If we can get locking to work, auto-busting a lock is almost trivial.
> Try to get the lock for n iterations, after that print anyway and
> complain "lock held too long".
> Give me a trylock() function and I'll give you auto-busting code.

Please, please, don't get fancy. There's no real problem, we've just
been doing too much cut and paste in the past without testing the new
code. This made us end up with different versions of printk, some with
locking, some without.
And, no, porting the code from v3 over is not an option at this point.
It does too much different stuff. Let's rather start dropping unneeded
implementations in v2 until things look sane again and then we can
decide what implementation we want.
>> We have made a decision that the BSP is always assumed to work. Any
>> strategy should be build around this assumption, and the further
>> assumption that we ought to contain the AP so that it can not prevent
>> the BSP from doing its job.
> Absolutely agreed. Auto-busting the lock would solve this nicely and
> even detect hangs.
I'm not sure I can interpret this into the above sentence. What would
lock auto-busting gain us? We'd be debugging printk, but nothing more?


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