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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Maxime,

On Mon, Feb 17, 2020 at 06:42:53PM +0100, Maxime Ripard wrote:
> 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.

This will create one issue though, in that the dual-link sinks are
supposed to have two input ports, in order to expose the odd and even
pixels ordering. If you have a single ouput port in your TCON, how will
you interface with such sinks ?

-- 
Regards,

Laurent Pinchart