[coreboot] Saving truncated preram CBMEM messages

[Paul Menzel]

Dear Nico,


Am Sonntag, den 08.01.2017, 15:23 +0100 schrieb Nico Huber:
> On 08.01.2017 14:38, Paul Menzel via coreboot wrote:

> > looking at the coreboot CBMEM console messages board status repository,
> > you’ll find a lot of truncated preram CBMEM console messages.
> > 
> > Currently the buffer size is 0xc00 – 3 kB, right –, which is too small
> > for quite some boards. The mainboard *Kabylake LPDDR3 RVP3* overrides
> > it to 0xd00.
> > 
> > So I am thinking about increasing it [1], but it’s of course not that
> > simple, especially as I don’t understand all the implications.
> > 
> > > Increasing this buffer reduces amount of available CAR stack, and
> > > apparently DDR3 raminit already struggles with the amount of
> > > cachelines available on fam10/15
> 
> This means a lower stack size (higher console buffer size) would result
> in a stack overflow. In other words, a brick.

One more question. How was the size 0xc00 chosen in the first place?

> > My first question is, what other downsides are there of increasing the
> > buffer size? I assume it’s unrelated to resulting usable RAM size, as
> > RAM sizes nowadays are much, much bigger? So would one megabyte be
> > reasonable/possible as a goal on boards supporting that?
> 
> No, no other downsides beside bricking.
> 
> > So if their is consensus that it should be increased, what would a way
> > be forward? I assume, overriding it per mainboard is not so useful, as
> > these messages are mostly from the chipset, so it should be chipset
> > dependent?
> 
> I would override it per chipset.

Understood. I adapted the change set accordingly for the Intel 945 [1].
Testers are welcome.

> But, for boards that implement the romstage main(), it has to be
> tested for each board (a single declaration in the main() could
> decide if the stack overflows or not).
> 
> A better option would be to reduce the verbosity: Identify log messages
> that are less useful (and could be hidden behind options like CONFIG_
> DEBUG_RAM_SETUP). Or something like disabling BIOS_SPEW messages if
> CBMEM is the only console.
>
> > Should that option be moved there?


Thanks,

Paul


> > [1] https://review.coreboot.org/18049/
> >    "arch/x86: Increase preram CBMEM console buffer size"
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: This is a digitally signed message part
URL: <http://www.coreboot.org/pipermail/coreboot/attachments/20170212/e0c114f6/attachment.asc>