On Tue, 26 Oct 2021 at 18:27, Simon Glass <s...@chromium.org> wrote: > > Hi Ilias, > > On Tue, 26 Oct 2021 at 08:06, Ilias Apalodimas > <ilias.apalodi...@linaro.org> wrote: > > > > Hi Simon, > > > > > + > > > > [...] > > > > > +This is why `CONFIG_OF_SEPARATE` should always be used when building > > > U-Boot. > > > +The `CONFIG_OF_EMBED` option embeds the devicetree somewhere in the > > > U-Boot ELF > > > +image as rodata, meaning that it is hard to find it and it cannot > > > increase in > > > +size. > > > + > > > +When modifying the devicetree, the different cases to consider are as > > > follows: > > > + > > > +- CONFIG_OF_SEPARATE > > > + This is easy, described above. Just change, replace or rebuild the > > > + devicetree so it suits your needs, then rerun binman or redo the > > > `cat` > > > + operation to join `u-boot-nodtb.bin` and the new `u-boot.dtb` > > > + > > > +- CONFIG_OF_EMBED > > > + This is tricky, since the devicetree cannot easily be located. If > > > the EFL > > > + file is available, then the _dtb_dt_begin and __dtb_dt_end symbols > > > can be > > > + examined to find it. While it is possible to contract the file, it > > > is not > > > + possible to expand the file since that would involve re-linking > > > + > > > +- CONFIG_OF_BOARD > > > + This is a board-specific situation, so needs to be considered on a > > > + case-by-case base. The devicetree must be modified so that the > > > correct > > > + one is provided to U-Boot. How this is done depends entirely on the > > > + implementation of this option for the board. It might require > > > injecting the > > > + changes into a different project somehow using tooling available > > > there, or > > > + it might involve merging an overlay file at runtime to obtain the > > > desired > > > + result. > > > > I thought this document was trying to describe the current situation in > > U-Boot. If so, the current CONFIG_OF_BOARD usage is far from what we have > > here. > > Can you be more specific? What is the difference here? Also see the > doc update later in the series, after OF_BOARD becomes a bool option.
The doc you sent says "devicetree must be modified so that the correct one is provided to U-Boot. By this I assume you mean the 'config/' node etc right? If that's the case this is *not* what is currently happening. We simply replace the entire device tree with whatever was configured. Regards /Ilias > > Regards, > SImon
