[yocto] [meta-raspberrypi] Adding an additional device tree overlay in the SDCard

[Herve Jourdain]

Hi Petter,

 

Thanks for your answers.

At some point, I’ve set it in the disto.conf – it works there – but for
maintenance reasons I’d love to be able to keep it “localized” with the
kernel .bbappend – since it clearly depends on the kernel.

 

For now, I’ve just patched the sdcard_image-rpi.bbclass, to take the
existing ${KERNEL_IMAGE}*.dtb in the ${DEPLOY_DIR_DIRECTORY}, split them in
overlay and non-overlay, and then do the processing like it’s done now.

It does work in my case, and I can provide the patch if it’s deemed of
interest. But I’m not sure whether or not there can be some side effects –
looks like rather safe, but more opinions are definitely needed on that.

 

Regarding the kernel, yes I’m using the 3.18 that is supported by the
meta-raspberry layer. As I mentioned in another thread, with more recent
kernels, the RaspberryPi overlay layers were added in a separate directory,
so in addition to a patch to build the newer kernel, the
sdcard_image-rpi.bbclass will also have to be modified to get the files in
the proper directory, when we switch to those newer kernels.

 

Best regards,

 

Herve

 

From: Petter Mabäcker [mailto:petter at technux.se] 
Sent: vendredi 31 juillet 2015 15:29
To: Herve Jourdain <herve.jourdain at neuf.fr>; francois at concept-embarque.fr;
Andrei Gherzan <andrei at gherzan.ro>
Cc: yocto at yoctoproject.org
Subject: Re: [yocto] [meta-raspberrypi] Adding an additional device tree
overlay in the SDCard

 

Hi Herve,

See inline answers.

BR,
Petter

On 07/30/2015 05:27 AM, Herve Jourdain wrote:

Hello,

 

I’m trying to add a specific .dts file to the raspberrypi.

Therefore, in my own layer, I have made a linux-raspberrypi_3.%.bbappend,
that applies a patch to the arch/arm/boot/dts makefile to add my own layer,
and a new rule that copies my specific .dts file to the kernel source
directory.

And, initially, I had also defined KERNEL_DEVICETREE += “myown-overlay.dtb”
in there.

 

It definitely compiles well, installation process is smooth, I get the
Image-myown-overlay.dtb in tmp/deploy/raspberrypi2.

 

BUT when I flash my SDCard, it does NOT appear in the “overlays” directory
of the DOS partition!

 

If I add it manually, everything works fine, so I know my overlay has been
correctly generated and is working.

 

What I discovered is that, the sdcard_image_rpi class takes the list of .dtb
to be considered from split_overlays(), which is defined in
linux-raspberrypi-base class.

And split_overlays() basically  gets the value of KERNEL_DEVICETREE (dts =
d.getVar("KERNEL_DEVICETREE", True)).

 

But when I set KERNEL_DEVICETREE in linux-raspberrypi_3.%.bbappend, it seems
the additional value it defines is NOT taken into account when
linux-raspberry-class evaluates the value of KERNEL_DEVICETREE.

I’ve checked in the create_image.rpi-sdimg script created, it does not
appear in DTS nor DT_OVERLAYS.

 

But when I define KERNEL_DEVICETREE in my distro.conf, THEN it is taken into
account


 

My goal would be to add that overlay by NOT modifying distro.conf (distros
are not necessarily RaspberryPi centric) nor in the raspberry machine files
(or local.conf).

This leads me to several questions:

#1 Is there a specific reason why my addition to KERNEL_DEVICETREE gets lost
when creating the image? I mean, is it normal, or are there some steps I
missed there?

Yes, in the current solution KERNEL_DEVICETREE is needed in both the kernel
recipe and image creation context. When appending KERNEL_DEVICETREE in
linux-raspberrypi_3.%.bbappend your new overlay will only be visible within
the linux-raspberrypi scope and NOT within the image class.




#2 Is there a way that I could achieve adding my .dtb overlay in the sdcard
image only from my linux kernel bbappend?


If I remember the code correct within the kernel scope we are only
interesting if device tree should be used. At least in theory (assuming you
are using a >= 3.18 kernel since then KERNEL_DEVICETREE will bve set by
default) you should be able to skip the KERNEL_DEVICETREE += code in
linux-raspberrypi_3.%.bbappend (since it will be set any way and the
overlays themselves isn't really used in here..) then append the
KERNEL_DEVICETREE within the image scope. If you don't want to put this into
the layer.conf or similiar in your own layer I guess it should work to
"prepend" for example the IMAGE_CMD. But in the current solution I guess
local.conf, layer.conf (in your own layer) or rpi-base.inc (in
meta-raspberrypi) is the easiest options..




#3 On a more general note, wouldn’t it be simpler (better?) to just add all
the .dtb that are found in the deploy/images/ directory to the DOS partition
of the SDCard? After all, the .dtb need to be compiled from a .dts, so all
the .dtb that appear in deploy/images are “legit”.


That might perhaps be a better solution. Have you tried it out? Andrei or
Francois might have some comments about this?



 

Herve





 

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