no dt overlay example in meta-skeleton

no dt overlay example in meta-skeleton

[dan]

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Hi,

In the  the meta-skeleton repo there is an example that shows how to build a standalone kernel module but no example of how to include or build an accompanying device tree overlay. Is there an existing "standard" way to achieve this? I am aware it can be done via the a .append on the linux kernel.

Many Thanks

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Re: [poky] no dt overlay example in meta-skeleton

[Richard Purdie]

On Thu, 2021-05-06 at 02:27 -0700, dan@engineeredarts.co.uk wrote:
> Hi, 
> 
> In the  the meta-skeleton repo there is an example that shows how to 
> build a standalone kernel module but no example of how to include or
> build an accompanying device tree overlay. Is there an existing "standard" way
> to achieve this? I am aware it can be done via the a .append on the linux kernel. 

I'm not aware of one but it would be something that could be nice to
add if you do work it out and were willing!

Cheers,

Richard

Re: [poky] no dt overlay example in meta-skeleton

[Quentin Schulz]

On Thu, May 06, 2021 at 10:35:55AM +0100, Richard Purdie wrote:
> On Thu, 2021-05-06 at 02:27 -0700, dan@engineeredarts.co.uk wrote:
> > Hi, 
> > 
> > In the  the meta-skeleton repo there is an example that shows how to 
> > build a standalone kernel module but no example of how to include or
> > build an accompanying device tree overlay. Is there an existing "standard" way
> > to achieve this? I am aware it can be done via the a .append on the linux kernel. 
> 
> I'm not aware of one but it would be something that could be nice to
> add if you do work it out and were willing!
> 

I agree on this.

Probably just need DEPENDS = "dtc-native" and do proper dtc calls in
do_compile.

I would expect this to be allarch too.

The tricky thing is that in order for dtbo to be usable, the original
dtb should keep the references of Device Tree nodes (which it does not
by default, or at least didn't, don't know for the more recent kernels).

See what I had to do for a project a while ago:
https://github.com/QSchulz/linux-at91/commit/c1ddbd31090bc8d82d5df38af2a12e8c053bb01f

I think we have support for DTC_FLAGS in Yocto now:
https://docs.yoctoproject.org/ref-manual/variables.html#term-KERNEL_DTC_FLAGS
so that could be a way to pass this flag without requiring users to patch the
sources of their Linux kernel.

Thinking about it, maybe that is something that could be added to
KERNEL_DTC_FLAGS if some other variable in set in, e.g. a machine
configuration file. Let's say KERNEL_DTBO_SUPPORT = "1" would add "-@"
to KERNEL_DTC_FLAGS.

Anyway, that's outside of the scope of the patch you could to send.

Just pointers :)

Looking forward to your patch,
Cheers,
Quentin

Re: no dt overlay example in meta-skeleton

[dan]

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RFC - this seems to work for me.

File : dtbo-standalone.bbclass
> 
> 
>> # Inherit this class in a recipe to build an out of kernel tree Device
>> tree overlay (.dtbo) file
> 
> 
>> DEPENDS = "dtc-native"
> 
> 
>> inherit deploy
> 
> 
>> do_compile() {
> 
> 
>> cd ${S}
> 
> 
>> pwd
> 
> 
>> for dtbo in ${DT_OVERLAYS}; do
> 
> 
>> dtc -@ -Hepapr -I dts -o $dtbo.dtbo $dtbo.dts
> 
> 
>> done
> 
> 
>> }
> 
> 
>> do_deploy() {
> 
> 
>> install -d ${DEPLOYDIR}
> 
> 
>> for i in ${S}/*.dtbo ; do
> 
> 
>> cp $i ${DEPLOYDIR}
> 
> 
>> done
> 
> 
>> }
> 
> 
>> addtask deploy before do_build after do_install
> 
> 
>> do_deploy[dirs] += "${DEPLOYDIR}"
> 
> 
>> PACKAGE_ARCH = "${MACHINE_ARCH}"
> 
> 

File : dtbo-standalone-image.bbclass

> 
> # Inherit this class in your image recipe to include Device tree overlay
> (.dtbo) files built outside of the kernel tree, e.g. by a my-dtbo.bb
> recipe
> 
> DTBO_STANDLONE ?= ""
> 
> def make_standalone_dtbo_files_list(d):
> # Generate IMAGE_BOOT_FILES entries for device tree files listed in
> # DTBO_STANDLONE.
> dtbs = d.getVar('DTBO_STANDLONE')
> 
> def transform(dtb):
> base = os.path.basename(dtb)
> if dtb.endswith('dtbo'):
> # overlay dtb:
> # eg: overlays/hifiberry-amp.dtbo has:
> #     DEPLOYDIR file: hifiberry-amp.dtbo
> #     destination: overlays/hifiberry-amp.dtbo
> return '{};{}'.format(base, dtb)
> elif dtb.endswith('dtb'):
> # eg: whatever/bcm2708-rpi-b.dtb has:
> #     DEPLOYDIR file: bcm2708-rpi-b.dtb
> #     destination: bcm2708-rpi-b.dtb
> return base
> 
> return ' '.join([transform(dtb) for dtb in dtbs.split(' ') if dtb])
> 
> IMAGE_BOOT_FILES += "${@make_standalone_dtbo_files_list(d)}"
> 

File : my-dtbo.bb

> 
> inherit dtbo-standalone
> 
> LICENSE = "CLOSED" # For brevity only
> SRC_URI += "file://my-dt.dts;subdir=${PN}-${PV}"
> DT_OVERLAYS = "my-dt"
> 

And then in the image where you want to install the DT file

> 
> DTBO_STANDLONE += "my-dt.dtbo"

> 
> inherit dtbo-standalone-image

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