GSoC 2020: Implementation of OFW functions

[Vijay Kumar Banerjee]

On Tue, May 5, 2020 at 10:40 PM Niteesh G. S. <niteesh.gs at gmail.com> wrote:

> This is thread is about implementing OFW functions in RTEMS as part
> of my GSoC project. I would like to start off with this part since the
> refactoring
> work will somewhat depend on this.
>
> Implementing these functions into RTEMS will make porting drivers from
> FreeBSD to RTEMS easy. Currently, the drivers ported from freebsd implement
> the functions using libfdt variants but this causes a lot of code
> duplication.
> eg: bsps/arm/imx/start/imx_iomux.c
>
> My initial thoughts were to implement these functions one by one. But then
> Christian and Vijay mentioned about porting them from libbsd. I went
> through the OFW code in libbsd and have described my porting process below.
> Please have a look at it and let me know if I have missed something or you
> would like to improve things.
>
> The following files will be ported from libbsd
> prefix = freebsd/sys/dev/ofw
> <prefix>/openfirm.c
> <prefix>/openfirm.h
> <prefix>/ofw_fdt.c
> <prefix>/ofwvar.h
>
> The main idea is to port openfirm.h but the other files are dependencies
> of openfirm.h
>
> Hi Niteesh,

The initial plan of your project was to implement the whole FDT support on
RTEMS,
but there's already support through libbsd, so it might be a better
solution to port any
remaining drivers from freebsd through libbsd and adapt the BSP drivers to
use the
freebsd FDT stack. This needs some discussion and input from other people
to form
the right plan and work accordingly.

After going through some open firmware documentation. I guess as far as
> RTEMS is
> concerned we could avoid many functions like OF_init, OF_putchar, OF_test
> and only care about functions defined under openfirm.h:105-142
>
> But these functions have dependency on the automatically generated
> ofw_if.h and KOBJS.
> But after a close inspection, I guess the KOBJSLOOKUP macro in ofw_if.h
> can be
> redefined or replaced for RTEMS. Since all it does is call the respective
> functions defined in ofw_fdt_methods(ofw_fdt.c).
>
> The openfirm.h is already ported in libbsd and is being used by some
driver ported
through libbsd (like i2c).
To help you understand the structure of the libbsd:
* The files in freebsd/ directory are already ported to RTEMS.
* The freebsd-org/ is the git submodule that has the original source of the
freebsd.
* The rtemsbsd/ has the codes that we added to adapt the freebsd codes.

The *_if.h files are generally automatically generated from the *_if.m
files.
The ofw_if.h has already been ported, you can find the generated header
file in rtemsbsd/include/rtems/bsd/local/ofw_if.h so there's no need to do
it
again. If future if there's a need to do it, we generally add a recipe to
build
the h files from the .m files in the Makefile.todo . You can have a look at
it
if you want, it's simple to follow.

I had just spent a few hours going through the code. If I had missed
> something
> please let me know.
>
> You're in the right direction. We need to wait a bit to get some input from
the community and progress accordingly.

Best regards,
Vijay

> Thanks,
> Niteesh.
>
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