Re: [Buildroot] [PATCH v2 1/1] configs/zynq_zc702_defconfig: new defconfig

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Neal,

On Tue, 31 Oct 2023 12:12:47 +0000
"Frager, Neal" <neal.frager@amd.com> wrote:

> I do understand your point.  From this perspective, we can say the
> same thing about the zynq_zed_defconfig and the
> zynq_microzed_defconfig as well.  For all 4 of these zynq boards, the
> DTS definition is all that changes from one defconfig to another.
> And in all 4 cases, the only differences in the dts files are things
> like gpio LEDs, switches and whether or not there is a CAN peripheral
> on board.  So you could potentially boot the same images across these
> boards.  You would just lose a peripheral or two that is included in
> one dts file but not another.

I think the discussion is not being specific enough here, so let me
provide some more background.

If the only differences between the zc706 and zc702 defconfigs is the
Linux kernel Device Tree (and I insist on Linux kernel Device Tree, not
Device Tree for the bootloaders/firmware), then you can have a single
configuration that builds multiple Device Trees, and the bootloader
selects the right one depending on which board we're booting on. This
is exactly what happens in beaglebone_defconfig:

BR2_LINUX_KERNEL_INTREE_DTS_NAME="am335x-evm am335x-bone am335x-boneblack am335x-bonegreen am335x-evmsk am335x-boneblue am335x-boneblack-wireless am335x-bonegreen-wireless"

We build multiple Linux kernel Device Trees, and the U-Boot bootloader
detects which board we boot on, and selects the right Device Tree.

If you are in this situation, then yes we want a single defconfig.

However, if the bootloader needs to be different on ZCU702 vs ZCU706,
and this difference is not detected at boot-time/run-time, but is
handled as a different build-time configuration, then you have no other
choice but to have 2 separate defconfigs.

Now I see this:

+BR2_TARGET_UBOOT_CUSTOM_TARBALL_LOCATION="$(call github,Xilinx,u-boot-xlnx,xlnx_rebase_v2023.01_2023.2)/xlnx_rebase_v2023.01_2023.2.tar.gz"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="xilinx_zynq_virt"
+BR2_TARGET_UBOOT_CUSTOM_MAKEOPTS="DEVICE_TREE=zynq-zc702"

in the ZCU702 defconfig, vs.

BR2_TARGET_UBOOT_CUSTOM_TARBALL_LOCATION="$(call github,Xilinx,u-boot-xlnx,xlnx_rebase_v2023.01_2023.2)/xlnx_rebase_v2023.01_2023.2.tar.gz"
BR2_TARGET_UBOOT_BOARD_DEFCONFIG="xilinx_zynq_virt"
BR2_TARGET_UBOOT_CUSTOM_MAKEOPTS="DEVICE_TREE=zynq-zc706"

Which means you need to have a different build-time configuration of
U-Boot, and therefore it's not possible to support both platforms in
the same Buildroot defconfig.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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