Re: import latest DTS files

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Fri, Jun 28, 2024 at 12:16:42PM +1200, Lloyd Parkes wrote:
> Kia ora koutou,
> I'm having a go at importing the latest DTS sources from kernel.org
> into my -current source tree so that I can get the latest DTS files for
> my Jetson Nano.
> 
> There seem to be some significant problems with the Linux code though. 
> 
> The biggest problem is a recent way the Linux people have been adding
> support for board variants. Here is an example.
> 
> A few months back DTS files were added for something called a Freebox
> containing an Amlogic Meson. There seem to be two variants of this
> board with either a Broadcom or Realtek Bluetooth chip. The DTS files
> are implemented as the following three files.
> 
>   * meson-g12a-fbx8am.dts
>   * meson-g12a-fbx8am-brcm.dtso
>   * meson-g12a-fbx8am-realtek.dtso
> 
> i.e. the board differences have been factored out into overlays. Fine,
> whatever.
> 
> The Makefile code the Linux folks have added is this.
> 
> 	dtb-$(CONFIG_ARCH_MESON) += meson-g12a-fbx8am-brcm.dtb
> 	dtb-$(CONFIG_ARCH_MESON) += meson-g12a-fbx8am-realtek.dtb
> 	
> 	# Overlays
> 	meson-g12a-fbx8am-brcm-dtbs     := meson-g12a-fbx8am.dtb
> meson-g12a-fbx8am-brcm.dtbo
> 	meson-g12a-fbx8am-realtek-dtbs  := meson-g12a-fbx8am.dtb
> meson-g12a-fbx8am-realtek.dtbo
> 
> The Linux Makefile in linux-6.9.6/scripts/Makefile.lib seems to know
> how to glue all this together and build all the named files, including
> merging the overlay and the base DTB into single DTB AFAICT. 
> 
> Have we dealt with this before? 

We haven't.  And when we have come close, large swaths of boards broke
to greater or lesser degrees because Linux didn't keep the new DTs compatible
with old drivers, and no one comprehensively tested the new import on all the
boards we run on.

My advice is don't touch things you can't comprehensively test.