GSOC: Adding FDT infrastructure to RTEMS

[Niteesh]

On Sun, Feb 2, 2020 at 2:55 PM Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> Hello Niteesh,
>
> I am not in favour of a home grown solution. We should not re-invent the
> wheel. Working with device trees may appear to be simple, however, this
> could end up in a multi-person-month project easily. There are several
> existing solutions for device drivers based on device trees. What are our
> requirements? For example compare the Zephyr approach to device trees
>
> https://docs.zephyrproject.org/latest/guides/dts/index.html
>
> with the one from Linux or FreeBSD. They are quite different.
>
> LK has also support for device trees:
>
> https://github.com/littlekernel/lk


I couldn't find any doc related to device trees for LK!

>
>
> I didn't find general support in FreeRTOS.
>
> The Zircon Device Model seems to be a bit too complex for RTEMS:
>
> https://fuchsia.dev/fuchsia-src/concepts/drivers/device-model
>
>
Thank you for all this information. I learned a lot of approaches to the
same problem. But how did you get all this information? Did you just google
it now? or is it from experience?


> For a GSoC project, the scope must be clear. We have to decide if we want
> do a dynamic approach (Linux and FreeBSD) or a static one (Zephyr).
>
> Most device trees are intended to be used by Linux. Some device trees have
> a horrible structure (e.g. for clock and IO pin configuration,
> cross-references between device nodes). Linux can deal with this. It has
> abilities to allow arbitrary cross-references within the tree (includes
> reference counting). FreeBSD lacks support for this. They use special case
> nasty hacks with global variables do deal with this.
>
> We already have device tree support for RTEMS in libbsd (port from
> FreeBSD). What could be a feasible GSoC project is to move this support to
> the main RTEMS repository. With the new build system this would be very
> easy. However, we don't talk about here of an import of a hand full of
> files. The FreeBSD device tree support depends on the general device/bus
> support, synchronization primitives, string handling, printing, logging,
> module concept (linker sets), etc.
>
> What we also have to keep in mind is that the current device driver
> initialization runs before multi-tasking with interrupts disabled. A
> dynamic device tree based initialization must be probably done in a proper
> task context.
>
> This project involves general RTEMS Project decisions about the future
> development roadmap.
>

Christian also said this, that's why I started this conversation even
though it is too early for GSoC. Can we all discuss the scope of the
project or if it is just too much for GSoC, I will look for some other
interesting ones.


> We also need a mentor with enough time for such a GSoC project.
>
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