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