Re: [Buildroot] [PATCH next v2 3/3] configs/raspberrypicm4io_64_uboot_defconfig: new defconfig

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

On Sat, Aug 31, 2024 at 09:01:26PM +0200, Fiona Klute via buildroot wrote:
> From: "Fiona Klute (WIWA)" <fiona.klute@gmx.de>
> 
> The new config deviates from the existing
> configs/raspberrypicm4io_64_defconfig only as far as necessary to
> demonstrate booting through U-Boot instead of having the firmware load
> the kernel directly. The sample boot script loads the kernel from the
> rootfs and uses the device tree provided by the firmware.
> 
> Signed-off-by: Fiona Klute (WIWA) <fiona.klute@gmx.de>
> ---
> The config I'm usually using is a bit different, including using a
> mainline kernel (which seems strongly preferable to me), but for
> defconfig maintenance staying close to the other RPi defconfigs is
> probably easiest.
> 
>  board/raspberrypi/boot.scr.in                 |  9 +++
>  .../raspberrypi/config_cm4io_64bit_uboot.txt  | 23 +++++++
>  board/raspberrypi/readme.txt                  |  4 ++
>  configs/raspberrypicm4io_64_uboot_defconfig   | 60 +++++++++++++++++++
>  4 files changed, 96 insertions(+)
>  create mode 100644 board/raspberrypi/boot.scr.in
>  create mode 100644 board/raspberrypi/config_cm4io_64bit_uboot.txt
>  create mode 100644 configs/raspberrypicm4io_64_uboot_defconfig
> 
> diff --git a/board/raspberrypi/boot.scr.in b/board/raspberrypi/boot.scr.in
> new file mode 100644
> index 0000000000..a5c986ef99
> --- /dev/null
> +++ b/board/raspberrypi/boot.scr.in
> @@ -0,0 +1,9 @@
> +# Please note that this is only a sample, we recommend you to change
> +# it to fit your needs. You should override this file using
> +# BR2_PACKAGE_HOST_UBOOT_TOOLS_BOOT_SCRIPT_SOURCE.
> +
> +# load kernel from the root partition
> +load mmc 0:2 ${kernel_addr_r} boot/Image
> +env set bootargs "root=/dev/mmcblk0p2 rootwait console=tty1 console=ttyAMA0,115200"
> +# boot using the FDT provided by firmware
> +booti ${kernel_addr_r} - ${fdt_addr}

Hello Fiona,

While I'm not a u-boot expert, I am slightly surprised to see a new
buildroot defconfig use boot.scr instead of extlinux.conf.

extlinux.conf is the default configuration format in u-boot:
https://github.com/u-boot/u-boot/blob/v2024.10-rc4/doc/develop/distro.rst?plain=1#L69-L71

Even though boot.scr still seems to be supported for backwards-compatibility:
https://github.com/u-boot/u-boot/blob/v2024.10-rc4/doc/develop/distro.rst?plain=1#L367-L368

See e.g. this buildroot commit that converted rock5b from boot.scr to
extlinux.conf:
https://github.com/buildroot/buildroot/commit/b7dbdd3d775b8e94664c6f37b11afc8a6a352e35

I don't see anthing exotic in your boot.scr that wouldn't work with
extlinux.conf.


Although I am I but confused why you set:
BR2_LINUX_KERNEL_INTREE_DTS_NAME="broadcom/bcm2711-rpi-cm4"
but then you do not use this device tree, but rather some
device tree provided by firmware.

What is the point of setting BR2_LINUX_KERNEL_INTREE_DTS_NAME if you
are not using this device tree?

I would strongly suggest to use the device tree that comes with the
kernel version that you are using, as the changes to the device tree
(to enable support for additional hardware in an existing SoC) might
often look different once upstreamed (compared to the downstream device
tree).


Kind regards,
Niklas
_______________________________________________
buildroot mailing list
buildroot@buildroot.org
https://lists.buildroot.org/mailman/listinfo/buildroot