[coreboot] locking...

Myles Watson mylesgw at gmail.com
Fri Jun 19 18:13:02 CEST 2009

> as we move into the multicore world, messages get harder and harder to
> read when they are interspersed byte-wise. I propose to add optional
> locking to printk.
This should only matter for the time during RAM, right?  Is it a larger

> However, this locking has to work when some CPUs are in CAR and others
> are in RAM. And that's the big problem.

> AFAICS we can't simply use atomic normal memory acceses since the CPUs
> in CAR won't see that. Atomic register modifications are not possible
> across processors AFAICS.
> The only idea I have is abusing some MMIO chipset/CPU space which is
> usable as scratch space. In theory, that should work. But do CPUs or
> chipsets have such MMIO areas?
They do.  It's hard to know if someone is already (ab)using them, though.

> Of course, I'm aware that locking (if possible at all) will be highly
> CPU/chipset dependent, but even if we can make locking work on only a
> subset of platforms, it is still a lot better than nothing.
Are you thinking of putting it in the ops of the cpu device?  I guess that
only works after CAR.

Another option would be to only let the BSP print messages by default.  That
would clean up most people's logs most of the time.


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