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

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Maxime Ripard <maxime@cerno.tech>
Cc: Chen-Yu Tsai <wens@csie.org>,
	dri-devel@lists.freedesktop.org,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Sean Paul <seanpaul@chromium.org>,
	Daniel Vetter <daniel.vetter@intel.com>,
	David Airlie <airlied@linux.ie>,
	devicetree@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Rob Herring <robh+dt@kernel.org>,
	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: Fri, 14 Feb 2020 17:49:53 +0200	[thread overview]
Message-ID: <20200214154953.GJ4831@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20200214154405.f5zuicm6uhhiczfs@gilmour.lan>

Hi Maxime,

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. 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.

-- 
Regards,

Laurent Pinchart