[PATCH 2/9] ARM: dts: socfpga: add Enclustra Intel AA1

[Marek Vasut]

On 9/27/24 12:53 AM, Lothar Rubusch wrote:
> On Thu, Sep 26, 2024 at 3:36 AM Marek Vasut <marex at denx.de> wrote:
>>
>> On 9/26/24 12:49 AM, Lothar Rubusch wrote:
>>
>> Hi,
> [...]
>>> Shall I add the files to my DTS patches and ask for upstreaming of the
>>> handoff files into the kernel?
>>
>> Are the handoff files really used by Linux for anything , or do they
>> contain various clock/pinmux/DRAM settings only used by U-Boot ? If the
>> later, place them into U-Boot and include them from -u-boot.dtsi file.
> 
> Similar to the other socfpga targets, the handoff files are just
> relevant to u-boot. So, I'll keep them in arch/arm/dts.

Right

> My particular situation then is as follows. The .dts file just
> includes several .dtsi files. I place this .dts file into
> arch/arm/dts. The first includes contain the "handoff setup". Then I
> include adjustments (.dtsi fragments) to the selected base-board and
> boot-mode. Both  can vary that's why I really would prefer to allow
> for a Kconfig option on that, in contrary to provide a set of .dts
> files for all possible combinations.
> 
> Example:
> $ cat ./arch/arm/dts/socfpga_arria10_mercury_aa1_pe1_sdmmc-u-boot.dts

Upstream DT named this way into Linux:

socfpga_arria10_mercury_aa1_pe1_sdmmc.dts

And then in U-Boot, implement the extras which include whatever you 
need, name the file:

socfpga_arria10_mercury_aa1_pe1_sdmmc-u-boot.dtsi

The U-Boot build system will combine the two DTs, the build system 
should automatically append matching -u-boot.dtsi content to any .dts file.

I am not sure if this also works if the .dts file is in dts/upstream/* 
while the -u-boot.dtsi is in arch/*/dts/ , but there is now definitely a 
use case for such a setup, it is probably a matter of tweaking the 
Makefiles .

> /dts-v1/;
> /* will be taken from /arch/arm/dts */
> #include "socfpga_arria10_mercury_aa1_handoff.h"
> #include "socfpga_arria10-handoff.dtsi"
> #include "socfpga_arria10_handoff_u-boot.dtsi"
> 
> /* will be taken from /dts/upstream */
> #include "../../../dts/upstream/src/arm/intel/socfpga/socfpga_arria10_mercury_aa1.dtsi"
> #include "../../../dts/upstream/src/arm/intel/socfpga/socfpga_enclustra_mercury_bootmode_sdmmc.dtsi"
> #include "../../../dts/upstream/src/arm/intel/socfpga/socfpga_enclustra_mercury_pe1.dtsi"
> 
> Ideally, now I like to have the first part as default device tree.
> DEFAULT_DEVICE_TREE=socfpga_arria10_mercury_aa1_pe1_sdmmc-u-boot.dts
> When doing so, I noticed I cannot enable CONFIG_OF_UPSTREAM anymore,
> the files in arch/arm/dts won't be found anymore.
> Then I have the issue how to access the generic .dtsi files used for
> boot-mode or base board. These files are identical to the kernel DT
> why I would prefer to use them from dts/upstream. Including them like
> ../../../../../... works, but... I think there must be a better way.

Look at how the -u-boot.dtsi are automatically added on top of .dts 
files, that might be a start.

> Ideally I like to setup some Kconfig choice for base board selection
> and one for boot-mode.

> 1.) In the documentation control.rst I read that the u-boot.dts is
> combined of several elements. Is there a way to take this base .dts,
> then add a base board .dtsi by Kconfig option, and similar a
> boot-mode?

The -u-boot.dtsi is preprocessed by C preprocessor, just like all the 
other DTs, so you can have a -u-boot.dtsi file which contains C 
preprocessor conditional statements in it to conditionally include other 
.dtsi files:

#if IS_ENABLED(...)
#include ...
#else ...
...
#endif

> 2.) Is there a way to enable CONFIG_OF_UPSTREAM and use explicit DTS
> from arch/arm/dts for the u-boot?

This I do not know.

> 3.) What would be the best possibility to have a u-boot.dts with
> handoff setup in arch/arm/dts and append .dtsi files from the general
> dts/upstream - in case are there other boards are doing something
> similar?

See above, maybe some of it helps.