Subject: Re: [PATCH v2 7/7] arm64: dts: allwinner: a64: enable ANX6345 bridge on Teres-I

From: Maxime Ripard <[email-masked]>
Date: Tue, 9 Jul 2019 10:55:32 +0200

On Mon, Jul 08, 2019 at 05:49:21PM -0700, Vasily Khoruzhick wrote:
> > > Maybe instead of edp-connector one would introduce integrator's specific
> > > connector, for example with compatible "olimex,teres-edp-connector"
> > > which should follow edp abstract connector rules? This will be at least
> > > consistent with below presentation[1] - eDP requirements depends on
> > > integrator. Then if olimex has standard way of dealing with panels
> > > present in olimex/teres platforms the driver would then create
> > > drm_panel/drm_connector/drm_bridge(?) according to these rules, I guess.
> > > Anyway it still looks fishy for me :), maybe because I am not
> > > familiarized with details of these platforms.
> >
> > That makes sense yes
>
> Actually, it makes no sense at all. Current implementation for anx6345
> driver works fine as is with any panel specified assuming panel delays
> are long enough for connected panel. It just doesn't use panel timings
> from the driver. Creating a platform driver for connector itself looks
> redundant since it can't be reused, it doesn't describe actual
> hardware and it's just defeats purpose of DT by introducing
> board-specific code.

I'm not sure where you got the idea that the purpose of DT is to not
have any board-specific code.

It's perfectly fine to have some, that's even why there's a compatible
assigned to each and every board.

What the DT is about is allowing us to have a generic behaviour that
we can detect: we can have a given behaviour for a given board, and a
separate one for another one, and this will be evaluated at runtime.

This is *exactly* what this is about: we can have a compatible that
sets a given, more specific, behaviour (olimex,teres-edp-connector)
while saying that this is compatible with the generic behaviour
(edp-connector). That way, any OS will know what quirk to apply if
needed, and if not that it can use the generic behaviour.

And we could create a generic driver, for the generic behaviour if
needed.

> There's another issue: if we introduce edp-connector we'll have to
> specify power up delays somewhere (in dts? or in platform driver?), so
> edp-connector doesn't really solve the issue of multiple panels with
> same motherboard.

And that's what that compatible is about :)

> I'd say DT overlays should be preferred solution here, not another
> connector binding.

Overlays are a way to apply a device tree dynamically. It's orthogonal
to the binding.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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