Re: [Buildroot] [PATCH v3 1/1] linux: make out-of-tree DTS work with newest kernels

[Michael Walle via buildroot <buildroot@buildroot.org>]

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On Wed Jan 22, 2025 at 11:52 AM CET, Arnout Vandecappelle wrote:
>
>
> On 22/01/2025 11:40, Romain Naour wrote:
> [snip]
> > The problem is that we define the path to the OOT dts file like this:
> > 
> > BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/at91-sama5d3_acqua.dts"
> > 
> > So we can't extract the vendor prefix from it even if it would look like this:
> > 
> > BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/acmesystems/acqua-a5/dts/microchip/at91-sama5d3_acqua.dts"
> > 
> > Note: the vendor prefix is not always one sub-directory:
> > 
> >    arch/arm/boot/dts/ti/omap/dra7.dtsi
> >    arch/arm64/boot/dts/exynos/google/gs101.dtsi
> > 
> > We probably need a new option to provide something like a dts "overlay"
> > BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY (similar to BR2_ROOTFS_OVERLAY) to copy a
> > dts directory directly to $(LINUX_ARCH_PATH)/boot/dts/
> > 
> >    BR2_LINUX_KERNEL_CUSTOM_DTS_OVERLAY="board/acmesystems/acqua-a5/dts"
> > 
> >    board/acmesystems/acqua-a5/dts/
> >    └── microchip
> >        └── at91-sama5d3_acqua.dts
> > 
> > Doing so, the BR2_LINUX_KERNEL_CUSTOM_DTS_PATH should be deprecated.
>
>   Alternatively, we can define an additional config variable 
> BR2_LINUX_KERNEL_CUSTOM_DTS_DIRECTORY that contains the subdirectory to which 
> the custom DTS is copied. So `microchip`, `ti/omap`, or `exynos/google`.
>
>   Disadvantage: we can't support multiple dts from different vendors.

As explained earlier, I'd aim for a solution which works in any
case.

> Not sure 
> if that is going to be an actual use case, but people do crazy things... But I 
> think for the common case (of only a single or a low number of DTSes that all 
> use the same CPU (family) so are in the same directory) it works well and is 
> much easier for the user.

The kernel supports multi (sub) arch. I'd prefer it if buildroot
would support the same. Think of an OEM who wants to build common
generic image shared between all its boards.

Esp. if it would be as 'easy' as splitting the current configuration
into a config for "/path/to/dts/files" and "list/of/board.dts
or/list/of/overlay.dtso". The later could also be the same option as
used for the in-tree kernel dts list. From a POV that might even be
easier. Also, the first option (which Romain calls _OVERLAY) could
also be a list, no?

-michael

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