[PATCH 00/21] Qualcomm generic board support

[Sumit Garg]

+ Linux kernel DT bindings maintainers, EBBR ML

On Thu, 30 Nov 2023 at 20:05, Tom Rini <trini at konsulko.com> wrote:
>
> On Thu, Nov 30, 2023 at 01:02:25PM +0530, Sumit Garg wrote:
> > On Wed, 29 Nov 2023 at 22:06, Neil Armstrong <neil.armstrong at linaro.org> wrote:
> > >
> > > On 29/11/2023 16:34, Caleb Connolly wrote:
> > > >
> > > >
> > > > On 23/11/2023 07:04, Sumit Garg wrote:
> > > >> On Wed, 22 Nov 2023 at 21:34, Caleb Connolly <caleb.connolly at linaro.org> wrote:
> > > >>>
> > > >>>
> > > >>>
> > > >>> On 22/11/2023 14:27, Tom Rini wrote:
> > > >>>> On Wed, Nov 22, 2023 at 07:44:09PM +0530, Sumit Garg wrote:
> > > >>>>> On Wed, 22 Nov 2023 at 19:31, Tom Rini <trini at konsulko.com> wrote:
> > > >>>>>>
> > > >>>>>> 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 at 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?
> > > >>>
> > > >>> For now, yes.
> > > >>
> > > >> But why? Is there any value added by larger u-boot specific DT (most
> > > >> of the nodes being unused by u-boot) than what currently u-boot
> > > >> supports? The more important part is to get alignment with Linux DT
> > > >> bindings. If you need to have memory/reserved-memory nodes in u-boot
> > > >> DT for generalization purposes then you should import those particular
> > > >> nodes only.
> > > >
> > > > I've been thinking about and hacking on this for the last week or so,
> > > > sorry for the delayed reply here.
> > > >
> > > > The value is in preventing any of the existing bindings from regressing,
> >
> > That is actually best addressed in Linux by checking the DTS against
> > yaml DT bindings. We don't have that testing available in u-boot and
> > only depend on careful reviews.
>
> I would absolutely love for someone to make another attempt at updating
> our kbuild infrastucture so that we can run the validation targets.
>

Given that EBBR requires [1] the platform (firmware/bootloader) and
not OS to supply the devicetree, it becomes evident that
firmware/bootloaders import DTS from Linux kernel (where it is
maintained).

But currently u-boot doesn't have a proper way to validate those DTS
against DT bindings (maintained in Linux kernel). Although there are
Devicetree schema tools available here [2], there isn't a versioned
release package of DT bindings which one should use to validate DTS
files.

@DT bindings maintainers,

Given the ease of maintenance of DT bindings within Linux kernel
source tree, I don't have a specific objection there. But can we ease
DTS testing for firmware/bootloader projects by providing a versioned
release package for DT bindings? Or if someone else has a better idea
here please feel free to chime in.

[1] https://arm-software.github.io/ebbr/#guiding-principles
[2] https://github.com/devicetree-org/dt-schema

-Sumit

> --
> Tom