On Thu, Jan 30, 2014 at 03:45:58PM -0500, Jason Cooper wrote:
> This is more of a process question: Is there any information captured
> in your EEPROM that can't be represented in the dtb? iow, at the point
> when you write the EEPROM, why not write the dtb to it as configured?
I can share what we do here.. In our systems the serial EEPROM is only
256 bytes, so storing things in DT format would be challenging.
What we do is have a master DTB that has the union of all our
configurations. The boot process has a very simple bit of code that
runs down the DTB in binary format and replaces entire
OF_DT_BEGIN_NODE->OF_DT_END_NODE regions with OF_DT_NOP.
The NOP approach is very simple, no other changes (eg offset
recalculation) needs to be done to the DT, so we can do this process
with a very small code footprint and without libfdt.
Choosing which sections to drop is done with some combination of
hardwired code and searching for specific property patterns. There are
also a few places where placeholder sections are directly fixed up, eg
a mac address is written into a placeholder of 0s, etc.
So an example might be
optional_peripheral@10000 {
orc,board-style = <1>;
[..]
}
Eg The board-style number comes from the EEPROM and if board-style !=
1 then the entire stanza is replaced with NOP.
Jason
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