Re: [Buildroot] [RFC PATCH 1/2] linux: install in-tree device-tree blob overlays

[Niklas Cassel via buildroot <buildroot@buildroot.org>]

Hello Gaël,

On Fri, Apr 12, 2024 at 04:09:44PM +0200, Gaël PORTAY wrote:
> The device-tree blob overlays are automatically built from the custom
> raspberrypi linux tree (for both architectures arm and arm64).
> 
> The device-tree overlays is mostly a downstream feature even though the
> upstream kernel generates the symbols node into the device-tree blobs it
> compiles (thanks to the option -@ in the DTC_FLAGS); and it does not
> have intree device-tree overlays.
> 
> Note: The device-tree overlays require the node __symbols__ to be part
> of the device-tree blob to get successfully loaded at runtime if the
> overlaied nodes make reference to symbols from the original devicetree
> blob.
> 
> The kernel image and the device-tree blobs for the raspberrypi boards
> are built from the downstream linux package, and the device-tree blob
> overlays are taken from the package rpi-firmware. Both packages linux
> and rpi-firmware have to be closely synced.
> 
> The buildroot tree maintains the packages and the board configurations,
> and it keeps things synced.
> 
> The downstream configurations in br2-external trees require to pay
> attention to that synchronization as well. If the files are out-of-sync,
> (i.e. the dtbos in the rpi-firmware package from the buildroot tree do
> not match the linux commit in the br2-external tree), then the boot may
> fail.
> 
> Since the Raspberry Pi's with Bluetooth have no dedicated debugging UART,
> they require to merge the bt-miniuart.dtbo to restore the UART0 to the
> accessible GPIOs of 40-pin GPIO header.
> 
> The investigation of the boot failure is comlicated if the root cause is
> due to the out-of-sync merge of the debugging uart's dtbo to the dtb and
> if firmware bootloader does not output the debug traces.
> 
> 	MESS:00:00:05.389885:0: brfs: File read: /mfs/sd/overlays/miniuart-bt.dtbo
> 	MESS:00:00:05.408881:0: dterror: can't find symbol 'uart1_bt_pins'
> 	MESS:00:00:05.411942:0: Failed to resolve overlay 'miniuart-bt'
> 
> All this long story to introduce the three new dtbos configs to build
> in-tree or out-of-tree dtbos, and to keep the directory name (assuming
> the downstream trees uses the directory name overlays).
> 
> The three configs are the equivalent to existing dts configs:
>  - BR2_LINUX_KERNEL_INTREE_DTS_OVERLAY_NAMES is equivalent to
>    BR2_LINUX_KERNEL_INTREE_DTS_NAME
>  - BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY_PATH is equivalent to
>    BR2_LINUX_KERNEL_CUSTOM_DTS_PATH
>  - BR2_LINUX_KERNEL_DTBO_KEEP_DIRNAME is equivalent to
>    BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME
> 
> Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>
> ---
>  linux/Config.in | 23 +++++++++++++++++++++++
>  linux/linux.mk  | 24 ++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/linux/Config.in b/linux/Config.in
> index 2767b709d4..fdd57e6ff9 100644
> --- a/linux/Config.in
> +++ b/linux/Config.in
> @@ -434,6 +434,29 @@ config BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT
>  	  Choose this option to support Device Tree overlays
>  	  on the target system.
> 
> +config BR2_LINUX_KERNEL_INTREE_DTS_OVERLAY_NAMES
> +	string "In-tree Device Tree Source Overlay file names"
> +	depends on BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT
> +	help
> +	  Name of in-tree device tree source file, without
> +	  the trailing -overlay.dts. You can provide a list of
> +	  dts files to build, separated by spaces.

I do not like that you assume that the DT overlay has a -overlay.dts suffix,
that seems to be something specific for the raspberry pi downstream kernel.

Most device tree overlays in the upstream kernel simply have a .dtso suffix:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=40658534756f8369e93b84fa75c20bde6528cb82

So it would be nice if your patch supported that as well.


Also see this other proposal from Michael Walle:
https://lore.kernel.org/buildroot/20240213154847.914068-1-michael@walle.cc/


Kind regards,
Niklas

> +
> +config BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY_PATH
> +	string "Out-of-tree Device Tree Source Overlay file paths"
> +	help
> +	  Paths to out-of-tree Device Tree Source Overlay (-overlay.dts)
> +	  and Device Tree Source Include (.dtsi) files, separated by
> +	  spaces. These files will be copied to the kernel sources and
> +	  the .dts files will be compiled from there.
> +
> +config BR2_LINUX_KERNEL_DTBO_KEEP_DIRNAME
> +	bool "Keep the directory name of the Device Tree Overlay"
> +	help
> +	  If enabled, the device tree blob overlays keep their
> +	  directory prefixes when they get copied to the
> +	  output image directory or the target directory.
> +
>  endif
> 
>  config BR2_LINUX_KERNEL_INSTALL_TARGET
> diff --git a/linux/linux.mk b/linux/linux.mk
> index 4e12b36c1f..8b3563394d 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -199,6 +199,14 @@ LINUX_DTS_NAME += $(basename $(filter %.dts,$(notdir $(call qstrip,$(BR2_LINUX_K
> 
>  LINUX_DTBS = $(addsuffix .dtb,$(LINUX_DTS_NAME))
> 
> +ifeq ($(BR2_LINUX_KERNEL_DTB_OVERLAY_SUPPORT),y)
> +LINUX_DTS_OVERLAY_NAMES += $(call qstrip,$(BR2_LINUX_KERNEL_INTREE_DTS_OVERLAY_NAMES))
> +
> +LINUX_DTS_OVERLAY_NAMES += $(basename $(filter %-overlay.dts,$(notdir $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY_PATH)))))
> +
> +LINUX_DTBOS = $(addsuffix .dtbo,$(LINUX_DTS_OVERLAY_NAMES))
> +endif
> +
>  ifeq ($(BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM),y)
>  LINUX_IMAGE_NAME = $(call qstrip,$(BR2_LINUX_KERNEL_IMAGE_NAME))
>  LINUX_TARGET_NAME = $(call qstrip,$(BR2_LINUX_KERNEL_IMAGE_TARGET_NAME))
> @@ -459,10 +467,23 @@ define LINUX_INSTALL_DTB
>  			$(1)/$(if $(BR2_LINUX_KERNEL_DTB_KEEP_DIRNAME),$(dtb),$(notdir $(dtb)))
>  	)
>  endef
> +define LINUX_INSTALL_DTBO
> +	$(foreach dtbo,$(LINUX_DTBOS), \
> +		install -D \
> +			$(wildcard $(LINUX_ARCH_PATH)/boot/dts/$(dtbo)) \
> +			$(1)/$(if $(BR2_LINUX_KERNEL_DTBO_KEEP_DIRNAME),$(dtbo),$(notdir $(dtbo)))
> +	)
> +endef
>  endif # BR2_LINUX_KERNEL_APPENDED_DTB
>  endif # BR2_LINUX_KERNEL_DTB_IS_SELF_BUILT
>  endif # BR2_LINUX_KERNEL_DTS_SUPPORT
> 
> +ifeq ($(BR2_LINUX_KERNEL_DTS_OVERLAY_SUPPORT),y)
> +define LINUX_BUILD_DTBO
> +	$(LINUX_MAKE_ENV) $(BR2_MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) $(LINUX_DTBOS)
> +endef
> +endif # BR2_LINUX_KERNEL_DTS_OVERLAY_SUPPORT
> +
>  ifeq ($(BR2_LINUX_KERNEL_APPENDED_DTB),y)
>  # dtbs moved from arch/$ARCH/boot to arch/$ARCH/boot/dts since 3.8-rc1
>  define LINUX_APPEND_DTB
> @@ -509,6 +530,7 @@ define LINUX_BUILD_CMDS
>  	$(LINUX_MAKE_ENV) $(BR2_MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) $(LINUX_TARGET_NAME)
>  	$(LINUX_BUILD_DTB)
>  	$(LINUX_APPEND_DTB)
> +	$(LINUX_BUILD_DTBO)
>  endef
> 
>  ifeq ($(BR2_LINUX_KERNEL_APPENDED_DTB),y)
> @@ -530,6 +552,7 @@ ifeq ($(BR2_LINUX_KERNEL_INSTALL_TARGET),y)
>  define LINUX_INSTALL_KERNEL_IMAGE_TO_TARGET
>  	$(call LINUX_INSTALL_IMAGE,$(TARGET_DIR)/boot)
>  	$(call LINUX_INSTALL_DTB,$(TARGET_DIR)/boot)
> +	$(call LINUX_INSTALL_DTBO,$(TARGET_DIR)/boot/overlays)
>  endef
>  endif
> 
> @@ -544,6 +567,7 @@ endef
>  define LINUX_INSTALL_IMAGES_CMDS
>  	$(call LINUX_INSTALL_IMAGE,$(BINARIES_DIR))
>  	$(call LINUX_INSTALL_DTB,$(BINARIES_DIR))
> +	$(call LINUX_INSTALL_DTBO,$(BINARIES_DIR))
>  endef
> 
>  ifeq ($(BR2_STRIP_strip),y)
> --
> 2.44.0
> 
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