Date:   Wed, 10 Jul 2019 13:40:42 +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 Tue, Jul 09, 2019 at 01:30:18PM -0700, Vasily Khoruzhick wrote:
> On Tue, Jul 9, 2019 at 1:55 AM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> >
> > 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.
>
> I believe DT was an attempt to move to declarative approach for
> describing hardware. Yes, we have different compatibles for different
> devices but they're specific to particular device rather than
> particular board. Device interconnection is described in DT along with
> some properties rather than in board-specific C-file.

You're right, but it's not incompatible with having some code to deal
with some board quirk.

> Introducing board-specific compatible for a connector isn't looking
> right to me.

If that board has a board-specific behaviour for it's connector, then
what's the issue?

You can't describe all the quirks in the all boards using purely
properties.

> > 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 :)
>
> Sorry, I fail to see how it would be different from using existing
> panels infrastructure and different panels compatibles. I think Rob's
> idea was to introduce generic edp-connector.

Again, there's no such thing as a generic edp-connector. The spec
doesn't define anything related to the power sequence for example.

> If we can't make it generic then let's use panel infrastructure.

Which uses a device specific compatible. Really, I'm not sure what
your objection and / or argument is here.

In addition, when that was brought up in the discussion, you rejected
it because it was inconvenient:
https://patchwork.freedesktop.org/patch/283012/?series=56163&rev=1#comment_535206

And I agree with you on that one.

> > > 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.
>
> It isn't orthogonal to original problem though.

It is. The original problem is that you want to power up whatever is
on the other side of a eDP link using an arbitrary regulator.

This is a "how do I describe that in my DT" problem, and it really has
nothing to do with how the DT is being passed to the kernel.

Maxime

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

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