Re: [Buildroot] [PATCH v2] linux: add support for device tree overlays

From: "Gaël PORTAY" <gael.portay@gmail.com>
To: "Fiona Klute" <fiona.klute@gmx.de>,
	"Michael Walle" <michael@walle.cc>, <buildroot@buildroot.org>
Cc: "Niklas Cassel" <Niklas.Cassel@wdc.com>,
	"Gaël PORTAY" <gael.portay@rtone.fr>,
	"Julien Grossholtz" <julien.grossholtz@openest.io>,
	"Damien Le Moal" <dlemoal@kernel.org>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Martin Bark" <martin@barkynet.com>
Subject: Re: [Buildroot] [PATCH v2] linux: add support for device tree overlays
Date: Mon, 02 Sep 2024 22:52:14 +0200	[thread overview]
Message-ID: <D3W3GXLAY046.CI48SHS5EP44@gmail.com> (raw)
In-Reply-To: <a9865fde-0c09-42dd-8cd2-d174412dce28@gmx.de>

All, thank you for your interest in bringing the support for dtbo!

On Mon Sep 2, 2024 at 4:32 PM CEST, Fiona Klute via buildroot wrote:
> > -LINUX_DTS_NAME += $(basename $(filter %.dts,$(notdir $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_PATH)))))
> > +LINUX_CUSTOM_DTS_PATH = $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_PATH))
> > +LINUX_DTS_NAME += $(basename $(filter %.dts,$(notdir $(LINUX_CUSTOM_DTS_PATH))))
> > +LINUX_DTSO_NAMES += $(basename $(filter %.dtso,$(notdir $(LINUX_CUSTOM_DTS_PATH))))
> >
> > -LINUX_DTBS = $(addsuffix .dtb,$(LINUX_DTS_NAME))
> > +LINUX_DTBS = $(addsuffix .dtb,$(LINUX_DTS_NAME)) $(addsuffix .dtbo,$(LINUX_DTSO_NAMES))
>
> This looks like the DTBOs will be installed to $BINARIES_DIR along with
> the DTBs. At least on RPi platforms it'd be preferable to be able to put
> them in an overlays/ directory, to make it easier to create the
> structure expected by the firmware in a genimage config without
> templating. I don't know how common this is across other platforms that
> use DT overlays.
>

IIRC, I have seen platforms that put the dtb and dtbo at the same place.

I strongly think the Pi is the one that put the dtbo in the subdirectory
overlays/.

> Would it be practical to add an option to install DTBOs in a
> (configurable) subdirectory?
>

Well, I do not really like adding an option to set the target directory.

In my patch serie I have completly split the dtbo from the dtb; so you
can keep or not the "top" directory for dtb (broadcom) and for dtbo
(overlays).

I do not think it worth it, but it helps for the Pi.

In the case of the Pi, you set:

	# BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME is not set
	BR2_LINUX_KERNEL_DTBO_KEEP_DIRNAME=y

To install dtbos to $BINARIES_DIR/overlays and dtb to $BINARIES_DIR.

	https://patchwork.ozlabs.org/project/buildroot/patch/20240902203533.3961108-2-gael.portay@rtone.fr/

I have no strong opinion about your work (more simple) and mine (more
duplication).

> Either way thank you for working on this!
>

Yes thank you (again).

> Best regards,
> Fiona
>

Kind Regards,
Gaël
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