Re: [Buildroot] Buildroot + u-boot + raspberry-pi Zero W

[uhmgawa <uhmgawa@third-harmonic.com>]

On 01/24/2024 12:25 PM, Peter Seiderer via buildroot wrote:

> Hello *,
>
> On Mon, 22 Jan 2024 12:31:58 -0500, uhmgawa <uhmgawa@third-harmonic.com> wrote:
>
>> I have a vanilla build of gitlab.com/buildroot.org/buildroot.git @ b200632b1ab for raspberrypi0w_defconfig
>> which seems fine directly booting the kernel using the stock Broadcom binary bootloader.  However
>> changing the Buildroot bootloader config to BR2_TARGET_UBOOT=y, several issues appear:
>> • While output/images/u-boot.bin is generated, it is not present in output/images/boot.vfat nor does the file /boot/config.txt reflect the expected launch of u-boot with "kernel=u-boot.bin" but rather remains set to directly boot the kernel zImage.
>
> The buildroot defconfigs are very minimal starting points for your own development
> (mostly simple booting with minimal feature set and console output/login via serial
> line)..., everything more special has to be done by (local) adjustments..., e.g. in
> your case:
>
> - providing an adjusted genimage.cfg (more straight forward before autogenerated,
>   see commit [1] and [2]) to include (additional) u-boot.bin to boot.vfat
>
> - providing an adjusted config.txt (see [1] and BR2_PACKAGE_RPI_FIRMWARE_CONFIG_FILE):
>
> 	enable_uart=1
> 	kernel=u-boot.bin

I actually tried the above as a direct modification of /boot/config.txt before my prior mail.
Still didn't resolve my issue (below).  Anyway after capturing the changes as prescribed
above, it took some rattling around to find a "make rpi-firmware-reinstall" was also required
to percolate the change into the buildroot's make scope. 

>
>
> After copying u-booot.bin manually to the boot partition and overwriting
> the config.txt my RPi zero w boots u-boot with the following output via serial line:
>
> 	U-Boot 2024.01 (Jan 24 2024 - 16:37:26 +0100)
>
> 	DRAM:  448 MiB
> 	RPI Zero W (0x9000c1)
> 	Core:  67 devices, 14 uclasses, devicetree: embed
> 	MMC:   mmc@7e202000: 0, mmc@7e300000: 1
> 	Loading Environment from FAT... Unable to read "uboot.env" from mmc0:1... 
> 	In:    serial,usbkbd
> 	Out:   serial,vidconsole
> 	Err:   serial,vidconsole
> 	Net:   No ethernet found.
> 	starting USB...
> 	Bus usb@7e980000: USB DWC2
> 	scanning bus usb@7e980000 for devices... 1 USB Device(s) found
> 	       scanning usb for storage devices... 0 Storage Device(s) found
> 	Hit any key to stop autoboot:  0 
> 	Card did not respond to voltage select! : -110
> 	No ethernet found.
> 	No ethernet found.

I'd hazard your config.txt doesn't have "dtoverlay=miniuart-bt" which was the root cause of my
issue as by default the miniuart is intended to serve as the u-boot console.  Once that's gone
both u-boot and the kernel (via u-boot bootargs) successfully speak to the miniuart.  I started
to get suspicious after realizing /boot/cmdline.txt contained "console=ttyAMA0,115200" which
was successfully booting the default kernel directly from the bootcode.bin/start.elf firmware.

> [1] https://gitlab.com/buildroot.org/buildroot/-/commit/e37ee5acdcebb59c0bcc89eca69540cea2ed441d
> [2] https://gitlab.com/buildroot.org/buildroot/-/commit/fc5cdeed724174d248dd1f979acea40af6e344ce
> [3] https://hechao.li/2021/12/20/Boot-Raspberry-Pi-4-Using-uboot-and-Initramfs/

All of the above was very helpful.  Thanks!

-john   (AKA '*')


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