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From:   Vasily Khoruzhick <anarsoul@gmail.com>
Date:   Wed, 10 Jul 2019 15:11:04 -0700
Message-ID: <CA+E=qVdFoT137pADfxz3uMwhOqjqrA9+6hBeOfbJxuH-M-3Pjw@mail.gmail.com>
Subject: Re: [PATCH v2 7/7] arm64: dts: allwinner: a64: enable ANX6345 bridge
 on Teres-I
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Andrzej Hajda <a.hajda@samsung.com>, Torsten Duwe <duwe@lst.de>,
        Harald Geyer <harald@ccbib.org>, Chen-Yu Tsai <wens@csie.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Icenowy Zheng <icenowy@aosc.io>,
        Sean Paul <seanpaul@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        devicetree <devicetree@vger.kernel.org>,
        arm-linux <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, Jul 10, 2019 at 4:40 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> 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@bootlin.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

It is inconvenient, but I don't understand how having board-specific
connectors fixes it.


> 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