[U-Boot] Board specific files

[Matthias Brugger]

On 03/04/2019 14:58, Alexander Dahl wrote:
> Hello Pascal,
> 
> Am Mittwoch, 3. April 2019, 09:08:57 CEST schrieb Linder Pascal:
>> I am new to U-Boot and I am trying to understand what I need to code for
>> using my own board with the bootloader.
> 
> Welcome. :-)
> 
> I try to describe my view on this, anyone correct me, if something is wrong.
> 
>> The device tree files I have already found under ./arch/arm/dts/. Can I just
>> add my device tree under this directory?
> 
> Yes. Note: you probably can not just copy a dts file from the Linux Kernel. 
> From what I discovered when adding a new board lately, those files are 
> slightly different.
> 
>> Also, what is the difference between the configuration files under
>> ./configs/ and ./include/configs/? Do I need to add a file in both of the
>> named directories?
> 
> For setting board options and more, U-Boot uses the Kconfig system from the 
> Linux kernel (adapted to the needs of U-Boot). In the old days everything was 
> set as preprocessor define in a board specific header in ./include/configs but 
> more and more options have been converted over the years.
> 
> Today you still need that header in ./include/configs but fewer things are set 
> there with each new U-Boot release.
> 

There is no documentation which config has to go into the include folder,
correct? I had a hard time to figure that out as well.

I suppose the situation here is the same as with DM, where we have boards and
drivers which are not yet converted. Do we have a roadmap to convert the legacy
configs to the new Kconfig system?

Regards,
Matthias

> The files in ./configs/ are default configs for a board to have an initial 
> working ./.config configuration file for that Kconfig approach. Although these 
> defconfigs are not strictly necessary, it's very convenient as a starting 
> point when compiling an image for a board. Some embedded build systems use 
> those defconfigs.
> 
>> If someone knows a well documented guide to add a new board to the mainline,
>> I would be very grateful.
> 
> I see two steps here. Getting all the things in place for a new board to boot 
> is one, the other one with a different set of challenges is getting that into 
> mainline U-Boot. 
> 
> For the first I would advise to look into ./README and ./doc/ (keep in mind, 
> information there might be outdated) and read lots of code of other boards, 
> preferably boards with a similar SoC added lately. 
> 
> For getting your patches into mainline, the guide on submitting patches in the 
> Linux kernel docs [1] mostly applies to U-Boot as well.
> 
> Greets
> Alex
> 
> [1] https://www.kernel.org/doc/html/latest/process/submitting-patches.html
> 
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