linux-kernel - Re: [PATCH/RFC 02/12] dt-bindings: display: renesas: lvds: Document renesas,swap-data

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Date:   Mon, 5 Aug 2019 12:35:43 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Fabrizio Castro <fabrizio.castro@...renesas.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Simon Horman <horms@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>
Subject: Re: [PATCH/RFC 02/12] dt-bindings: display: renesas: lvds: Document
 renesas,swap-data

Hi Fabrizio,

On Mon, Aug 05, 2019 at 08:59:51AM +0000, Fabrizio Castro wrote:
> > From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Sent: 02 August 2019 08:44
> > Subject: Re: [PATCH/RFC 02/12] dt-bindings: display: renesas: lvds: Document renesas,swap-data
> > 
> > Hi Fabrizio,
> > 
> > Thank you for the patch.
> > 
> > On Fri, Aug 02, 2019 at 08:33:59AM +0100, Fabrizio Castro wrote:
> > > R-Car D3, R-Car E3, and RZ/G2E support dual-link mode.
> > > In such a mode, the first LVDS encoder emits even data, and the
> > > second LVDS encoder emits odd data. This patch documents property
> > > renesas,swap-data, used to swap even and odd data around.
> > >
> > > Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> > > ---
> > >  Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> > b/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> > > index dece79e..8980179 100644
> > > --- a/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> > > +++ b/Documentation/devicetree/bindings/display/bridge/renesas,lvds.txt
> > > @@ -52,6 +52,11 @@ Optional properties:
> > >    mandatory for the first LVDS encoder on R-Car D3, R-Car E3, and RZ/G2E SoCs,
> > >    and shall point to the second encoder to be used as a companion in dual-link
> > >    mode. It shall not be set for any other LVDS encoder.
> > > +- renesas,swap-data : when in dual-link mode, the first LVDS encoder normally
> > > +  emits even data, and the second LVDS encoder emits odd data. When property
> > > +  renesas,swap-data is specified, the data emitted by the two encoders will be
> > > +  swapped around. This property can only be used in conjunction with property
> > > +  renesas,companion.
> > 
> > From an LVDS encoder point of view this is more a configuration option
> > than a description of the hardware. Wouldn't it be better for the LVDS
> > sink to report which of the odd or even pixels it expects on each of its
> > endpoints ?
> 
> Yes, that would be my preference too, and it would be better, I am just not entirely
> what's the best place for this information though
> 
> > The LVDS encoder driver could then query that at runtime and
> > configure itself accordingly. Ideally this should be queried through the
> > drm_bridge_timings structure (or through a similar mean), not through
> > DT. An LVDS sink that has a fixed mapping of odd/even pixels to
> > endpoints wouldn't need the information to be specified in DT at all.
> 
> Isn't drm_bridge_timings specific for bridges?

Its name makes it specific to bridges, but the information it contains
could equally apply to panels. I would thus use it for both, possibly
after renaming it.

-- 
Regards,

Laurent Pinchart