Re: [PATCH 1/3] dt-bindings: display: add bindings for MIPI DBI compatible SPI panels

[Maxime Ripard <maxime@cerno.tech>]

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Hi Rob,

On Mon, Jan 24, 2022 at 10:42:37AM -0600, Rob Herring wrote:
> On Mon, Jan 24, 2022 at 10:28 AM Noralf Trønnes <noralf@tronnes.org> wrote:
> >
> >
> >
> > Den 24.01.2022 17.08, skrev Rob Herring:
> > > On Sun, Jan 23, 2022 at 11:25 AM Noralf Trønnes <noralf@tronnes.org> wrote:
> > >>
> > >> Add binding for MIPI DBI compatible SPI panels.
> > >
> > > I'm sure we already have MIPI DBI panels. What's this for?
> > >
> >
> > It aims to use one driver to cover all MIPI DBI panels where the
> > controller setup is loaded from userspace in a firmware file.
> 
> What's the solution when the user wants a splash screen in the
> bootloader and also wants multiple panels supported?
> 
> Also, 1 driver doesn't dictate 1 compatible. A one to many
> relationship is fine and makes the decision entirely the OS's.
> 
> > The cover
> > letter points to the discussion where Maxime proposed this:
> >
> > https://lore.kernel.org/dri-devel/20211129093946.xhp22mvdut3m67sc@houat/
> 
> The proposal there is:
> 
> > compatible = "panel-spi";
> > model = "panel-from-random-place-42";
> 
> The same thing can be accomplished with this:
> 
> compatible = "panel-from-random-place-42", "panel-spi";
> 
> What's the advantage of hijacking 'model'?

So, the main issue is that a panel is essentially two things: a
controller and the actual panel.

The controller has an initialization sequence of its own, and part of it
is parameters to match the panel.

So you can have identical controllers that won't have the same
initialization sequence because they don't have the same panel.

I was assuming that a compatible would be more about the controller, so
we needed something else, thus "model"

Maxime

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