[coreboot] [RFC]What to do with TINY_BOOTBLOCK?

Kyösti Mälkki kyosti.malkki at gmail.com
Mon Oct 24 20:37:18 CEST 2011


On Mon, 2011-10-24 at 10:22 -0600, Marc Jones wrote:
> On Mon, Oct 24, 2011 at 4:15 AM, Patrick Georgi <patrick at georgi-clan.de> wrote:
> > Hi all,
> >
> > as you may be aware, coreboot has two different ROM layouts so far.
> >
> > The older one is derived from what we did before CBFS, and has all code that
> > does RAM init (our "romstage") in the bootblock (up to 64k at the top end of
> > the image). This worked for a long time, but required some hackery for
> > supporting dual-image scenarios (like fallback/normal, where we normal
> > passed control to fallback by jumping to start-8 bytes), and it also broke
> > when AMD's RAM setup became so complicated that it doesn't fit in 64k
> > anymore.
> > Those 64k are mandated by ROM mappings of various chipsets which, by
> > default, only provide access to the upper 64k.
> >
> > The newer one, created after the CBFS switch and exploiting its features,
> > has a tiny bootblock (hence the name), often less than 1k, which implements
> > some policy: By default, it simply looks up "fallback/romstage" in CBFS and
> > executes it. Our other policy does the old fallback/normal routine (using a
> > counter in nvram), but executing files in CBFS as well, instead of jumping
> > into the void and hoping that there's code there.
> >
> > The problem with the new approach is that it requires full ROM mapping
> > rather early. Boards whose romstage fit in the 64k were free to defer
> > setting up mapping to whereever it is convenient inside the romstage, so
> > it's not all that easy to identify without means to test it. Unfortunately,
> > this is a runtime problem, not a build problem, so it's hard to test all our
> > 160 boards. For this reason, we kept both mechanisms in the tree, under the
> > monikers BIG_BOOTBLOCK and TINY_BOOTBLOCK.
> >
> > Some chipsets that are in common use were converted rather early, so by now,
> > 100 boards use tiny bootblock, while 60 use the old method.
> > Since then - not much happened.
> >
> > Kyösti Mälkki recently brought this issue up again (thanks!), and proposes
> > to invert the flags, making tiny bootblock the default, so "big" bootblock
> > has to be requested explicitely and also adding some "maybe" flag for boards
> > that might just work. This is quite a large change, but I fear it'll bring
> > relatively little progress - people will just copy the TINY_NO_BOOTBLOCK (or
> > what it's called in the latest patch iteration) flag and move on.
> >
> > Therefore, I propose (http://review.coreboot.org/#change,320) to get rid of
> > the "big bootblock" variant altogether. This might break some boards
> > (silently: they still build, but they fail on boot), but at least it forces
> > action to fix them.
> >
> > Advantages:
> > - one flag less to care about
> > - more uniform feature set (big bootblock didn't support any fallback
> > mechanism)
> > - more opportunities to clean out and simplify the build system and code -
> > there are some crude workarounds to make both mechanisms work
> >
> > Disadvantages:
> > - Boards might be broken for a long time until someone tries them again. The
> > visible result is that the boot fails early (ie. no error signalling at all,
> > the system simply hangs, nothing visible).
> >
> > It's possible to determine all boards that _might_ be affected (those that
> > use a big bootblock now), so I could add that list to the commit message,
> > hopefully helping whoever stumbles over this issue.
> >
> > Comments?
> >
> 
> Hi Patrick,
> 
> I think that this makes sense. It seems like the change would improve
> the build and standardize early coreboot. I think that we can support
> developers in the porting for those platforms when they come up. The
> ROM decode is a typically a southbridge setting, so do you know what
> southbridges would be untested?
> 
> Marc
> 
> 

Hello Marc

I am glad this topic brings up discussion.

List of mainboards that currently do not select TINY_BOOTBLOCK 
and do not select ROMCC in Kconfig:

aaeon/pfm-540i_revb
amd/db800
amd/norwich
amd/rumba
artecgroup/dbe61
asus/a8v-e_deluxe
asus/a8v-e_se
asus/mew-am
asus/mew-vm
bcom/winnetp680
digitallogic/msm800sev
ecs/p6iwp-fe
hp/e_vectra_p2706t
iei/pcisa-lx-800-r10
intel/eagleheights
intel/mtarvon
jetway/j7f24
lenovo/x60
lippert/frontrunner
lippert/hurricane-lx
lippert/literunner-lx
lippert/roadrunner-lx
lippert/spacerunner-lx
mitac/6513wu
msi/ms6178
nec/powermate2000
pcengines/alix1c
pcengines/alix2d
roda/rk886ex
traverse/geos
tyan/s2735
via/epia-cn
via/epia-m700
via/pc2500e
winent/pl6064
wyse/s50

List of southbridges on those mainboards, as taken from the
mainboard/Kconfig files.

SOUTHBRIDGE_AMD_CS5535
SOUTHBRIDGE_AMD_CS5536
SOUTHBRIDGE_INTEL_I3100
SOUTHBRIDGE_INTEL_I82801AX
SOUTHBRIDGE_INTEL_I82801EX
SOUTHBRIDGE_INTEL_I82801GX
SOUTHBRIDGE_INTEL_I82870
SOUTHBRIDGE_RICOH_RL5C476
SOUTHBRIDGE_TI_PCI7420
SOUTHBRIDGE_VIA_K8T890
SOUTHBRIDGE_VIA_VT8237R

It appears all but the two below already have an implementation with
tiny bootblock on some other mainboard:

SOUTHBRIDGE_AMD_CS5535
SOUTHBRIDGE_AMD_CS5536

It may be that the only reason BIG_BOOTBLOCK gets dragged along, is that
there has been no clear migration path away from it. I think there now
exists a better choice, pushing the choice in menuconfig.

http://review.coreboot.org/333


As a side note. I did not realise it was possible to have TINY_BOOTBLOCK
without Cache-As-Ram. There was no such implementation (besides QEMU).
I thought that tiny bootblock would also move memory controller
initialisation away from romstage (so it could be compiled with gcc) and
then utilise cache for its stack.

KM







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