Hi Romain,

On Mon, 19 Aug 2024 at 01:15, Romain Crausaz crausaz.romain@gmail.com wrote:

Hi Simon, Hi Peter,

First of all, thanks a lot for your answers.

1. When I enable the i2c bus in the config.txt (which is parsed by the rpi first stage bootloader), the overlay put this as compatible:"brcm,bcm2835". I checked in the source of U-Boot and the driver is not available.
2. One solution could be to use the i2c-gpio driver instead of the default i2c controller. U-Boot has this driver.
3. Since the device tree passed by the rpi bootloader is stored in the variable fw_dtb_pointer (see the lowlevel_init.S) would I be able to do the following: 3.1 remove the automatic selection for the device tree passed by the rpi bootload 3.2 system starts and use the default device tree where the i2c bus is defined with i2c-gpio, access the device I need and store the information needed 3.3 get the device tree address from fw_dtb_pointer, set fdt address fdt addr with the new device tree and then start the kernel

I have another question, what triggers the DM to check for the device (with dm tree command there is a X under the column probed). Because here we could have a really simple device tree with the minimum configuration for just the i2c and load it from U-Boot, perform the action needed and then boot the kernel by passing the device tree provided by the first stage bootloder.

Just a little niggle, please avoid top-posting as it messes up the history for later readers.

U-Boot devices are probed when used. So you could use the 'i2c' command to make it be probed.

Regards, Simon

Regards Romain

Le sam. 17 août 2024 à 17:57, Simon Glass sjg@chromium.org a écrit :

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+Peter Robinson +Matthias Brugger

Hi Romain,

On Sat, 17 Aug 2024 at 07:01, Romain Crausaz crausaz.romain@gmail.com wrote:

...

Hi all,

I am currently facing an issue with U-Boot and a raspberry pi CM4. Here is the setup:

1. Yocto Scarthgap

2. U-Boot 2024.01

3. rpi_arm64_defconfig

I am trying to access the i2c bus from U-Boot. I have been trying to modify the device tree which is referenced as “CONFIG_DEFAULT_DEVICE_TREE="bcm2711-rpi-4-b”” in the defconfig without success. I can remove everything, set all nodes to disabled and I see no change in U-Boot (I am using dm commands to check the status of the peripherals).

It seems that with the rpi, U-Boot will only configure itself against the device tree passed by the bootloader of RPI. Could someone confirm this ?

Yes. It isn't quite obvious, but this is a clue:

Core: 211 devices, 16 uclasses, devicetree: board

'board' means that the board can do whatever it wants.

...

Is there a way to configure / modify U-Boot to use its own devicetree and simply pass the device tree generated by the rpi bootloader to the kernel ?

Because the second issue is that the i2c driver defined in the device tree passed to u-boot is not available in u-boot.

Thanks for your help

Since OF_HAS_PRIOR_STAGE is a hidden option, you cannot disable it in the defconfig. The only way I know of is to comment out the 'imply OF_HAS_PRIOR_STAGE' in ARCH_BCM283X in arch/arm/Kconfig

For me, that stops the rpi_4 booting, so perhaps the devicetree is out-of-date or ft_board_setup() is doing something strange, or something else. The in-tree devicetree may have got out-of-date, so perhaps use the Linux one.

Regards, Simon