[Buildroot] [Proposal] Build RPi dtbo overlays instead of just copying

[Scott Ellis <scott@jumpnowtek.com>]

> BTW, if there is a make rule for .dtbo, have you tried simply adding
> your list of .dtbo of interest to BR2_LINUX_KERNEL_USE_INTREE_DTS ?
>

Its a little awkward, but I think it will work.

I had to add the 'overlays/' path to the dts name for the kernel
build to see it

For example

  BR2_LINUX_KERNEL_INTREE_DTS_NAME="bcm2710-rpi-3-b overlays/pwm-with-clk-overlay"

This is the same thing you have to do manually if you don't use the
'make dtbs' target.

scott at fractal:~/rpi/linux$ make pwm-with-clk.dtbo
make: *** No rule to make target 'pwm-with-clk.dtbo'.  Stop.

scott at fractal:~/rpi/linux$ make pwm-with-clk-overlay.dtbo
make: *** No rule to make target 'pwm-with-clk-overlay.dtbo'.  Stop.

scott at fractal:~/rpi/linux$ make overlays/pwm-with-clk.dtbo
make: *** No rule to make target 'overlays/pwm-with-clk.dtbo'.  Stop.

scott at fractal:~/rpi/linux$ make overlays/pwm-with-clk-overlay.dtbo
make: *** No rule to make target 'overlays/pwm-with-clk-overlay.dtbo'.  Stop.

scott at fractal:~/rpi/linux$ make overlays/pwm-with-clk-overlay.dtb
...
DTC     arch/arm/boot/dts/overlays/pwm-with-clk-overlay.dtb


The overlay that's generated has the name 'pwm-with-clk-overlay.dtb'

So it still has to be renamed for the RPi to use it as an overlay

  pwm-with-clk-overlay.dtb -> pwm-with-clk.dtbo

And it has to be copied to the boot partition 'overlays/' directory.

But this can all be handled in a post-xxx script.

Unless there is a better suggestion, I'll play around with doing
it this way instead.

Thanks.

Best regards,
Scott

"Thomas Petazzoni" <thomas.petazzoni@free-electrons.com> said:

> Hello,
> 
> On Wed, 18 Jan 2017 14:32:46 -0500 (EST), Scott Ellis wrote:
>> Currently RPi dtbo overlays come from the rpi-firmware package and are
>> just copies of the binaries built upstream.
>>
>> The source for the dtbos are in the same github.com/raspberrypi/linux
>> tree that Buildroot is using for the kernel and the main board dtb.
> 
> Indeed.
> 
>> I'm suggesting the overlay dtbos should be in sync with the kernel
>> and the main dtb we are using and get built at the same time.
>>
>> The particular problem I want to solve is to allow my modifications
>> to overlays or addition of new overlays both via standard kernel patches
>> get built and installed into the image.
> 
> Makes sense.
> 
>> I understand this is an RPi specific change to linux.mk, so I'm asking
>> first whether it is of interest and worthwhile submitting a patch.
> 
> Indeed the below is too RPi specific in my opinion. If we want to merge
> a solution, it has to be more generic, which is difficult to achieve
> because there are no overlays in the upstream Linux kernel so there is
> nothing that shows what should be the "standard" way of
> storing/building overlays.
> 
>> +ifeq ($(BR2_LINUX_KERNEL_DTS_OVERLAYS_SUPPORT),y)
>> +define LINUX_INSTALL_DTB_OVERLAYS
>> +       cp $(KERNEL_ARCH_PATH)/boot/dts/overlays/*.dtbo $(1)
> 
> Perhaps the location where the .dtbo are produced should be
> configurable, since it's not a standardized behavior that they end up
> in arch/ARCH/boot/dts/overlays/ ?
> 
>>  ifeq ($(BR2_LINUX_KERNEL_APPENDED_DTB),y)
>> @@ -350,6 +357,10 @@ define LINUX_BUILD_CMDS
>>         @if grep -q "CONFIG_MODULES=y" $(@D)/.config; then      \
>>                 $(LINUX_MAKE_ENV) $(MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) modules ; 
>>       \
>>         fi
>> +       $(if $(BR2_LINUX_KERNEL_DTS_OVERLAYS_SUPPORT),
>> +               $(LINUX_MAKE_ENV) $(MAKE) $(LINUX_MAKE_FLAGS) -C $(@D) dtbs ;    
>>       \
>> +       )
> 
> I'm not sure how to handle that one. It doesn't relate only to overlay
> support, but also to regular Device Trees. It is actually going to
> build all Device Trees that are enabled for the currently selected
> kernel configuration.
> 
> BTW, if there is a make rule for .dtbo, have you tried simply adding
> your list of .dtbo of interest to BR2_LINUX_KERNEL_USE_INTREE_DTS ?
>
>> @@ -390,6 +403,8 @@ endef
>>  define LINUX_INSTALL_IMAGES_CMDS
>>         $(call LINUX_INSTALL_IMAGE,$(BINARIES_DIR))
>>         $(call LINUX_INSTALL_DTB,$(BINARIES_DIR))
>> +       mkdir -p $(BINARIES_DIR)/rpi-firmware/overlays
>> +       $(call LINUX_INSTALL_DTB_OVERLAYS,$(BINARIES_DIR)/rpi-firmware/overlays)
> 
> This rpi-firmware reference is clearly too RPi specific to be in
> linux.mk.
> 
> Thomas
> --
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com
>