Re: [PATCH 1/2] dt-bindings: display: sun4i-tcon: Add LVDS Dual Link property

From: Maxime Ripard <maxime@cerno.tech>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org, David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org, Chen-Yu Tsai <wens@csie.org>,
	Rob Herring <robh+dt@kernel.org>,
	Sean Paul <seanpaul@chromium.org>,
	Daniel Vetter <daniel.vetter@intel.com>,
	Frank Rowand <frowand.list@gmail.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] dt-bindings: display: sun4i-tcon: Add LVDS Dual Link property
Date: Mon, 17 Feb 2020 18:42:53 +0100	[thread overview]
Message-ID: <20200217174253.mj53us4bb7h2lyca@gilmour.lan> (raw)
In-Reply-To: <20200214154953.GJ4831@pendragon.ideasonboard.com>

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On Fri, Feb 14, 2020 at 05:49:53PM +0200, Laurent Pinchart wrote:
> On Fri, Feb 14, 2020 at 04:44:05PM +0100, Maxime Ripard wrote:
> > On Fri, Feb 14, 2020 at 03:10:25PM +0200, Laurent Pinchart wrote:
> > > On Fri, Feb 14, 2020 at 01:32:43PM +0100, Maxime Ripard wrote:
> > > > SoCs that have multiple TCONs can use the two set of pins on the first TCON
> > > > to drive a dual-link display. Add a property to enable the dual link.
> > > >
> > > > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > > > ---
> > > >  .../bindings/display/allwinner,sun4i-a10-tcon.yaml         | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/allwinner,sun4i-a10-tcon.yaml b/Documentation/devicetree/bindings/display/allwinner,sun4i-a10-tcon.yaml
> > > > index 86ad617d2327..aa6dd8409dbc 100644
> > > > --- a/Documentation/devicetree/bindings/display/allwinner,sun4i-a10-tcon.yaml
> > > > +++ b/Documentation/devicetree/bindings/display/allwinner,sun4i-a10-tcon.yaml
> > > > @@ -105,6 +105,13 @@ properties:
> > > >          - const: edp
> > > >          - const: lvds
> > > >
> > > > +  allwinner,lvds-dual-link:
> > > > +    type: boolean
> > > > +    description: |
> > > > +      On a SoC with two TCON with LVDS support, the first TCON can
> > > > +      operate over both pins sets to output in a dual-link setup. This
> > > > +      will be triggered by setting this property.
> > >
> > > Could you maybe provide an example of how this property is supposed to
> > > be used ? I'm especially wondering what ports are used in that case and
> > > how they're connected.
> >
> > It's pretty trivial to support, it's only a property to set on the
> > encoder node itself.
> >
> > I'm not really sure what you meant by your question with the ports
> > though :/
>
> I assume that, in the single-link case, you have two TCON instances that
> operate independently, each of them with one port that models an LVDS
> connection to a panel.

Indeed,

> In the dual-link mode, how does that look like ? Does the TCON
> instance that operate in dual-link mode have two ports in DT ? There
> are two physical ports, so I think it makes sense to always have two
> ports in DT. That's what we're doing for the LVDS encoders on R-Car
> Gen3, in order to specify in DT which LVDS input of the dual-link
> panel is connected to which LVDS output of the SoC. That allows
> configuring the LVDS encoder to send the even and odd pixels on the
> right port.

As far as I can tell, you can't control that in our TCON. It just on
more lanes, that's it. Also, we currently have multiple ports, to map
another feature of the TCON, which is that it can drive directly a
panel, or will send its output to the HDMI / TV encoders. Adding
another port in that will break the current binding we have.

Maxime

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