DT overlay issues - dtc flags

[Frank Rowand]

adding cc to myself so I will see replies.


On 04/10/17 09:16, Andreas Färber wrote:
> Hi,
> 
> I've tried to play around with Device Tree overlays (.dtbo files):
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/overlay-notes.txt
> 
> First of all, that document refers to a non-existing
> Documentation/devicetree/dt-object-internal.txt. Could someone please
> fix that one way or another?
> 
> In my particular example I've tried to extend the &i2c1 and &gpio nodes
> of 4.11-rc5 arm64 broadcom/bcm2837-rpi-3-b.dts. The above documentation
> prominently claims that this can be done via target = <&foo> syntax, but
> U-Boot's fdt apply command fails for such a file. If instead I use the
> alternative target-path = "/soc/..." then it works just fine.
> 
> As mentioned in the very bottom of the documentation, resolution of
> phandle target references requires a __symbols__ node in the base .dtb.
> IIUC this is only generated when passing the -@ dtc command line flag.
> 
> At first I thought this were an issue with how we build the .dtb files
> in openSUSE [1], but by my reading of the kernel Makefiles not passing
> -@ in DTC_FLAGS or cmd_dtc, you should run into the exact same issue.
> 
> I could think of a few ARMv7-M systems where such DT bloat might be
> undesired (small flash sector sizes), but then it would seem easier to
> suppress -@ where needed than to have a feature that by all practical
> means is half unusable by default.
> 
> U-Boot itself appears to face a similar issue in that its internal
> Device Trees are built without -@, and via Alex' distro boot extensions
> this internal DT is passed on via UEFI as fallback when no external .dtb
> file is found. So in the non-SPL case the DT should probably be built
> with -@, too.
> 
> Or am I misunderstanding something here?
> 
> Thanks,
> Andreas
> 
> [1]
> https://build.opensuse.org/package/view_file/Kernel:HEAD/dtb-aarch64/dtb-aarch64.spec?expand=1
>