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

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

[Herve Jourdain]

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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?

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

#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".

 

Herve


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

[Petter Mabäcker]

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

[Francois Muller]

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Hi,
My comment below.
Best regards,
François

Le vendredi 31 juillet 2015 à 15:29 +0200, Petter Mabäcker a écrit :
> 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..
If modifying *.inc / *.conf files is not an option, then I would give a
try to Petter's suggestion to create a new image recipe (or bbappending
the current one). I see no reason this shouldn't do the trick, while
still being easy.
> 
>     
> 
>     > > 
> >       > > 
> >         
> > 
> >         > > #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?
As far as I can remember, deploy/images/ links are only updated (meaning created if not previously present, updated if a new artefact is available) but never removed. This implies that if you simply copy 'deploy/images/*-overlay.dtb'  to the sdcard, your image may end up with some devicetree overlays that are potentially no longer wanted or (even worse) not to be used with the specific kernel that will boot up the board...
That's the reason why I think choosing consciously the devicetree (overlay) set to pack in the sdcard may be important.

> 
>     > 
>     > > 
> >       > > 
> >         
> > 
> >         > >  
> > 
> >         > > Herve
> > 
> >       
> > 
> >       
> > 
> >       > > 
> >       
> > 
> >     
> 
>     
> 
>   
> 
> 

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

[Herve Jourdain]

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

[Herve Jourdain]

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Hi François,

 

Well, if the .dtb might not get removed, like you describe, then changing the sdcard_image-rpi.bbclass the way I do might for sure create issues at some point.

It works for me – obviously – but definitely can’t be generalized.

Thanks for the insight :)

 

Best regards,

 

Herve

 

From: Francois Muller [mailto:forlorn18@gmail.com] 
Sent: vendredi 31 juillet 2015 17:16
To: Petter Mabäcker <petter@technux.se>; Herve Jourdain <herve.jourdain@neuf.fr>; Andrei Gherzan <andrei@gherzan.ro>
Cc: yocto@yoctoproject.org
Subject: Re: [yocto] [meta-raspberrypi] Adding an additional device tree overlay in the SDCard

 

Hi,

 

My comment below.

 

Best regards,

François

 

Le vendredi 31 juillet 2015 à 15:29 +0200, Petter Mabäcker a écrit :

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..

 

If modifying *.inc / *.conf files is not an option, then I would give a try to Petter's suggestion to create a new image recipe (or bbappending the current one). I see no reason this shouldn't do the trick, while still being easy.

 





#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?

 

As far as I can remember, deploy/images/ links are only updated (meaning created if not previously present, updated if a new artefact is available) but never removed. This implies that if you simply copy 'deploy/images/*-overlay.dtb'  to the sdcard, your image may end up with some devicetree overlays that are potentially no longer wanted or (even worse) not to be used with the specific kernel that will boot up the board...

That's the reason why I think choosing consciously the devicetree (overlay) set to pack in the sdcard may be important.

 

 

Herve





 


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

[Petter Mabäcker]

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Hi,

BR,
Petter

On 08/01/2015 03:22 AM, Herve Jourdain wrote:
>
> 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.
>
Feel free to either send a RFC patch to the mailinglist or start by 
sending it for early feedback to me, Andrei and Alex.
>
> 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.
>
I remember that thread. We are currently working with integrating 4.x 
into meta-raspberrypi you can follow Alex work at 
http://redmine.gherzan.com/issues/62. One problem is however how to 
handle support for both 3.x and 4.x with the current KERNEL_DEVICETREE 
solution in combination with the changed overlay directories.
>
> Best regards,
>
> Herve
>
> *From:*Petter Mabäcker [mailto:petter@technux.se]
> *Sent:* vendredi 31 juillet 2015 15:29
> *To:* Herve Jourdain <herve.jourdain@neuf.fr>; 
> francois@concept-embarque.fr; Andrei Gherzan <andrei@gherzan.ro>
> *Cc:* yocto@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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