[PATCH 1/2] opos6uldev: make the LCD work again

[Sumit Garg]

+ Shawn, Krzysztof, Conor

Hi Tom,

On Wed, 28 Feb 2024 at 18:40, Tom Rini <trini at konsulko.com> wrote:
>
> On Wed, Feb 28, 2024 at 10:09:13AM +0300, Dan Carpenter wrote:
> > On Tue, Feb 27, 2024 at 04:40:01PM +0100, Sébastien Szymanski wrote:
> > > Commit 5d7a95f49999 ("imx6ul/imx6ull: synchronise device trees with
> > > linux") removed the display timings from the board device tree whereas
> > > they are still needed by the mxsfb driver.
> > > Add the timings back (the correct ones) in the
> > > imx6ul-opos6uldev-u-boot.dtsi file and remove them from the
> > > opos6uldev.env file.
> > >
> > > Update the opos6uldev_defconfig file so that the LCD turns on at boot.
> > >
> > > Fixes: 5d7a95f49999 ("imx6ul/imx6ull: synchronise device trees with linux")
> > > Signed-off-by: Sébastien Szymanski <sebastien.szymanski at armadeus.com>
> >
> > Huh.  This is the commit that did that upstream.
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d9aa4d4fca67823838fe9861456201430c545e69
> >
> > It's interesting how the timings in linux were always slightly different
> > from in u-boot.
>
> Thanks for tracking that down, Dan. I'm adding in Sumit and Rob here
> because this is a recent (rather than ancient) example of one of the
> concerns about OF_UPSTREAM.

I rather think about this as an opportunity to improve with
OF_UPSTREAM. We can feed these kinds of DT ABI breakages to
corresponding Linux kernel sub-arch maintainers. Especially once we
move to OF_UPSTREAM and a sub-arch maintainer profile in Linux kernel
to keep them aware that U-Boot should be considered too.

> I think the commit in question can be
> summarized as "remove a bunch of explicit HW information because there's
> now a Linux Kernel driver that determines that dynamically". What do we
> do next? The old information is in a presumably valid binding still, can
> we just put it back and comment that consumers outside of Linux use this
> still so it's not removed again later? Or am I just missing where we can
> instead get this information from the DT still and not need to come up
> with a new driver and subsystems?

I can see following two paths forward:

1) Partially revert the Linux kernel commit to add back the display
timings in DT.
2) Extend drivers/video/simple_panel.c in U-Boot to add support for
compatible: "armadeus,st0700-adapt".

If possible then I would be in favour of (2) rather than the current
patch to do this properly.

-Sumit

>
> --
> Tom