linux-kernel - RE: [PATCH v3 1/8] dt-bindings: display: Add bindings for LVDS bus-timings

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Message-ID: <OSBPR01MB176683A6508892FBF1159FEDC0A20@OSBPR01MB1766.jpnprd01.prod.outlook.com>
Date:   Thu, 29 Aug 2019 09:14:37 +0000
From:   Fabrizio Castro <fabrizio.castro@...renesas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <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>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Sam Ravnborg <sam@...nborg.org>
Subject: RE: [PATCH v3 1/8] dt-bindings: display: Add bindings for LVDS
 bus-timings

Hi Geert,

Thank you for your feedback!

> From: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> On Behalf Of Geert Uytterhoeven
> Sent: 29 August 2019 08:58
> Subject: Re: [PATCH v3 1/8] dt-bindings: display: Add bindings for LVDS bus-timings
> 
> Hi Fabrizio,
> 
> On Wed, Aug 28, 2019 at 8:36 PM Fabrizio Castro
> <fabrizio.castro@...renesas.com> wrote:
> > Dual-LVDS connections need markers in the DT, this patch adds
> > some common documentation to be referenced by both panels and
> > bridges.
> >
> > Signed-off-by: Fabrizio Castro <fabrizio.castro@...renesas.com>
> 
> Thanks for your patch!
> 
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/bus-timings/lvds.yaml
> > @@ -0,0 +1,38 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/display/bus-timings/lvds.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Common Properties for bus timings of LVDS interfaces
> > +
> > +maintainers:
> > +  - Thierry Reding <thierry.reding@...il.com>
> > +  - Fabrizio Castro <fabrizio.castro@...renesas.com>
> > +
> > +description: |
> > +  This document defines device tree properties common to LVDS and dual-LVDS
> > +  interfaces, where a dual-LVDS interface is a dual-link connection with even
> > +  pixels traveling on one connection, and with odd pixels traveling on the other
> > +  connection.
> > +  This document doesn't constitue a device tree binding specification by itself
> > +  but is meant to be referenced by device tree bindings.
> > +  When referenced from panel or bridge device tree bindings, the properties
> > +  defined in this document are defined as follows. The panel and bridge device
> > +  tree bindings are responsible for defining whether each property is required
> > +  or optional.
> > +
> > +properties:
> > +  dual-lvds-even-pixels:
> > +    type: boolean
> > +    description:
> > +      This property is specific to an input port of a sink device. When
> > +      specified, it marks the port as recipient of even-pixels.
> > +
> > +  dual-lvds-odd-pixels:
> > +    type: boolean
> > +    description:
> > +      This property is specific to an input port of a sink device. When
> > +      specified, it marks the port as recipient of odd-pixels.
> 
> Do you need the "dual-" prefix? Isn't that implied by even/odd?
> Or is it better to keep it, for readability?

I decided to go with "dual-lvds-even-pixels" and "dual-lvds-odd-pixels"
because the "dual-lvds" prefix uniquely identifies the type of bus, and I
decided to go with the "pixels" suffix because "dual-lvds-odd" just doesn't
sound right. I guess "dual-lvds-even-pixels" and "dual-lvds-odd-pixels"
are the most readable and future proof labels I could think of, but maybe
there is something better we can do? Laurent?

> 
> I'm also thinking about a possible future extension to triple or quad LVDS.
> As I'm not aware of English word equivalents of even/odd for triple/quad,
> perhaps this should be specified using a numerical value instead?

I would have to see a use case for other LVDS configurations for providing
a proper answer to this question, but perhaps we could accept that other
configurations for LVDS connections may come with labels that are tailored
to help uniquely identifying the ports while being readable? Perhaps numerical
values would work better in other cases? Laurent?

> 
> If I go too far, please just say so ;-)

Definitely worth discussing!

Thanks,
Fab

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds