Date:   Tue, 9 Jul 2019 10:55:32 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Vasily Khoruzhick <anarsoul@...il.com>
Cc:     Andrzej Hajda <a.hajda@...sung.com>, Torsten Duwe <duwe@....de>,
        Harald Geyer <harald@...ib.org>, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Sean Paul <seanpaul@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        arm-linux <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/7] arm64: dts: allwinner: a64: enable ANX6345 bridge
 on Teres-I

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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