Re: [PATCH 00/21] Qualcomm generic board support

[Tom Rini <trini@konsulko.com>]

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On Wed, Nov 22, 2023 at 11:51:29AM +0530, Sumit Garg wrote:
> Hi Caleb,
> 
> On Tue, 21 Nov 2023 at 22:39, Caleb Connolly <caleb.connolly@linaro.org> wrote:
[snip]
> > == DT loading ==
> >
> > Previously, boards used the FDT blob embedded into U-Boot (via
> > OF_SEPARATE). However, most Qualcomm boards run U-Boot as a secondary
> > bootloader, so we can instead rely on the first-stage bootloader to
> > populate some useful FDT properties for us (notably the /memory node and
> > KASLR seed) and fetch the DTB that it provides. Combined with the memory
> > map changes above, this let's us entirely avoid configuring the memory
> > map explicitly.
> 
> Since with this change, we don't need to embed FDT blob in the u-boot
> binary, so I was thinking if we really need to import DTs from Linux
> for different platforms and then play a catchup game?
> 
> IMO, the build command would look like following if we import
> pre-built FDT blob from Linux:
> 
> - Build u-boot::
> 
>        $ export CROSS_COMPILE=<aarch64 toolchain prefix>
>        $ make qcom_defconfig
>        $ make
> 
> - gzip u-boot::
> 
>        gzip u-boot-nodtb.bin
> 
> - Append dtb to gzipped u-boot::
> 
>         cat u-boot-nodtb.bin.gz
> <linux-tree>/arch/arm64/boot/dts/qcom/your-board.dtb >
> u-boot-nodtb.bin.gz-dtb
> 
> This would avoid the maintenance burden to keep DT in sync with that
> of Linux. And since DT bindings in Linux are backwards compatible, we
> can say u-boot should work with DTB picked up from any Linux kernel
> stable release.

I guess one question I have is, are we being passed the device tree
(since we're acting like the Linux Kernel) or knowing that we have the
dtb attached to the end of us and making use of the old kernel appended
dtb option? We're fine in for example the rpi_arm64 case of just being
given a device tree from the previous stage and not needing one in-tree.

-- 
Tom

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