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

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Date:   Thu, 06 Jun 2019 15:59:27 +0200
From:   Harald Geyer <harald@...ib.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
cc:     Torsten Duwe <duwe@....de>, Vasily Khoruzhick <anarsoul@...il.com>,
        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>,
        Andrzej Hajda <a.hajda@...sung.com>,
        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

Guys, this discussion is getting heated for no reason. Let's put
personal frustrations aside and discuss the issue on its merits:

Maxime Ripard writes:
> On Wed, Jun 05, 2019 at 12:13:17PM +0200, Torsten Duwe wrote:
> > On Tue, Jun 04, 2019 at 08:08:40AM -0700, Vasily Khoruzhick wrote:
> > > On Tue, Jun 4, 2019 at 5:23 AM Torsten Duwe <duwe@....de> wrote:
> > > >
> > > > Teres-I has an anx6345 bridge connected to the RGB666 LCD output, and
> > > > the I2C controlling signals are connected to I2C0 bus. eDP output goes
> > > > to an Innolux N116BGE panel.
> > > >
> > > > Enable it in the device tree.
> > > >
> > > > Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> > > > Signed-off-by: Torsten Duwe <duwe@...e.de>
> > > > ---
> > > >  .../boot/dts/allwinner/sun50i-a64-teres-i.dts      | 65 ++++++++++++++++++++--
> > > >  1 file changed, 61 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64-teres-i.dts b/arch/arm64/boot/dts/allwinner/sun50i-a64-teres-i.dts
> > > > index 0ec46b969a75..a0ad438b037f 100644
> > > > --- a/arch/arm64/boot/dts/allwinner/sun50i-a64-teres-i.dts
> > > > +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64-teres-i.dts
> > > > @@ -65,6 +65,21 @@
> > > >                 };
> > > >         };
> > > >
> > > > +       panel: panel {
> > > > +               compatible ="innolux,n116bge", "simple-panel";
> > >
> > > It's still "simple-panel". I believe I already mentioned that Rob
> > > asked it to be edp-connector.

Actually just dropping the "simple-panel" compatible would be a poor
choice. Even if "edp-connector" is specified as binding and implemented in a
driver, there are older kernel versions and other operating systems to
keep in mind. If the HW works with "simple-panel" driver satisfactorily,
we should definitely keep the compatible as a fall back for cases where
the edp-connector driver is unavailable.

If think valid compatible properties would be:
compatible = "innolux,n116bge", "simple-panel";
compatible = "edp-connector", "simple-panel";
compatible = "innolux,n116bge", "edp-connector", "simple-panel";
compatible = "edp-connector", "innolux,n116bge", "simple-panel";

I can't make up my mind which one I prefere. However neither of these
variants requires actually implmenting an edp-connector driver. And each
of these variants is clearly preferable to shipping DTs without
description of the panel at all and complies with bindings after adding
a stub for "edp-connector".

> And the DT is considered an ABI, so yeah, we will witheld everything
> that doesn't fit what we would like.

I fail to see how the patch in discussion adds new ABI. While I understand
the need to pester contributors for more work, outright blocking DTs, that
properly describe the HW and comply with existing bindings, seems a
bit unreasonable. (Assuming there are no other issues of course.)

Also note that the innolux,n116bge binding suggestes using simple-panel
as fallback.

HTH,
Harald

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