[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
> <c-d.hailfinger.devel.2006 at gmx.net> 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