Re: [coreboot] SPD binaries in coreboot

[Nico Huber]

On 23.10.2015 21:54, Aaron Durbin wrote:
> On Fri, Oct 23, 2015 at 2:43 PM, Carl-Daniel Hailfinger
>  wrote:
> > On 23.10.2015 21:15, Martin Roth wrote:
> > > I like what I understand Nico's proposal to be: Store the SPD data as
> > > a c struct with all of the different JEDEC fields broken out.  it
> > > would relatively trivial to compile this into an SPD binary, or it can
> > > be used in whatever other fashion is desired.  A tool to convert from
> > > a binary SPD to the structure file would be desirable to help the
> > > transition, but it's out of the build path.

Thanks for the support. One remark: I would really prefer serializing
during runtime over compiling a C struct to a binary. The latter could
cause much bit-field headache given the SPD format.
> > > I believe this satisfies all the requirements:
> > > It's easy to review differences.
> > > It can be be built with no new tools.
> > > The fields are broken out, so you can actually tell what you're doing.
> >
> > Now that would be a nice way to combine the benefits of diffable source
> > and no-tool builds.
> >
> > Ron, is that solution is acceptable to you?
> >
> > Side note: There is a tool called decode-dimms which can be fed with
> > binary SPD dumps. It decodes everything in the SPD and could serve as a
> > nice way to verify the output of Ron's magic SPD tool.
>
> Do people realize these binaries sit in cbfs?

Yes, they do _currently_. We don't have to keep it that way.
> Are we going to compile
> random c files into object files then objcopy them? Then add to cbfs?

I wouldn't like that either.
> Also, the SPD format is quite silly as it is w.r.t. values crossing
> multiple fields in a byte, etc. There's not really a good way to
> encode that in a C struct.

We don't have to encode the binary SPD format in the C struct. We can
just use a C struct to store the SPD information. Like we used C structs
before we knew bit fields (wasn't that a good time?). If we encounter a
not so beautiful, unchangeable interface that needs the information as
binary SPD, well, we could decide to be gracious and serialize the in-
formation.

Nico