Re: [PATCH 05/21] ARM: dts: omap: Bind panel to panel-dpi instead of ti,tilcdc,panel driver

[Kory Maincent <kory.maincent@bootlin.com>]

On Tue, 2 Dec 2025 13:51:59 +0200
Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> wrote:

> Hi Kory,
> 
> On 02/12/2025 13:18, Kory Maincent wrote:
> > On Tue, 2 Dec 2025 11:47:40 +0100
> > Krzysztof Kozlowski <krzk@kernel.org> wrote:

> I will not NAK, removing bindings and breaking users is under some
> conditions acceptable. You just need to come with the reasons and impact.
> 
> Reason "is ugly" is usually not good enough. Especially if things were
> working.

Thanks for you reply.

> >>
> >> DTS cannot go to drm, which means you either need to separate the change
> >> and make entire work bisectable and backwards compatible for some time
> >> OR at least document clearly the impact as we always ask.  
> > 
> > The thing is, if I split it, it has to be in 3. One for the of DRM bus flags
> > support, a second for the the devicetree and binding change and a third for
> > the whole tilcdc and tda998x cleaning stuff. I think I will go for one
> > series, with better documentation.
> > 
> > Now, what is your point of view on my question. Will you nak any binding
> > removal even if the binding is ugly and legacy and imply maintaining an
> > non-standard tilcdc panel driver? I know it breaks DTB compatibility but
> > there is several argument to not keep it. See patch 6.  
> The binding being ugly and having to maintain non-standard tilcdc panel
> driver may be nice things for us, the users don't care. The users care
> if their board no longer works.

Yes I understand but then I have another question. At what cost should we
continue to support legacy binding?

Just figured out this case already happened, ti,tilcdc,slave binding was
removed from the tilcdc driver:
739acd85ffdb7 ("drm/tilcdc: Remove obsolete "ti,tilcdc,slave" dts binding
support")

Even if there is still one mainline device tree that uses it:
am335x-base0033.dts. :/

> And how does this sync with u-boot? It also has code for at least for a
> few of these boards.

U-boot has indeed a driver for the ti,tilcdc,panel binding.
Changing this devicetree would beak display for these board in U-boot as it
currently does not support the "panel-dpi" binding.

> Are there even users for these boards? If not, maybe they can be just
> removed? I'm personally not familiar with these boards, so I have no
> idea of their age or distribution.

These boards are quite old (>10 years) but I don't know if they are still used
by people. After a quick look they seem not available on the market.

> One trick that can be done is to modify the loaded DTB at boot time,
> detecting the old format, converting it to the new one, so that when the
> drivers are probed they only see the new DTB.

Yes, indeed that could do the trick. The things is, I don't have one of
theses board to test it. I will try to look for an other way to test it.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com