linux-kernel - RE: [PATCH v3 0/8] Add dual-LVDS panel support to EK874

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Message-ID: <TYXPR01MB17753318ECA1556FE53C262AC0680@TYXPR01MB1775.jpnprd01.prod.outlook.com>
Date:   Tue, 22 Oct 2019 16:30:07 +0000
From:   Fabrizio Castro <fabrizio.castro@...renesas.com>
To:     Laurent Pinchart <Laurent.pinchart@...asonboard.com>
CC:     Sam Ravnborg <sam@...nborg.org>, Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Chris Paterson <Chris.Paterson2@...esas.com>,
        Biju Das <biju.das@...renesas.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        "ebiharaml@...linux.co.jp" <ebiharaml@...linux.co.jp>,
        Fabrizio Castro <fabrizio.castro@...renesas.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>,
        Andrzej Hajda <a.hajda@...sung.com>
Subject: RE: [PATCH v3 0/8] Add dual-LVDS panel support to EK874

Hi Laurent,

Did you have any time to look into this series?

Thanks,
Fab

> From: Fabrizio Castro <fabrizio.castro@...renesas.com>
> Sent: 28 August 2019 19:37
> Subject: [PATCH v3 0/8] Add dual-LVDS panel support to EK874
> 
> Dear All,
> 
> this series adds support for dual-LVDS panel IDK-2121WR
> from Advantech:
> https://buy.advantech.eu/Displays/Embedded-LCD-Kits-High-Brightness/model-IDK-2121WR-K2FHA2E.htm
> 
> V3 approaches the problem in a completely different way, we now
> have two new properties to mark the ports in the DT as receiving
> even pixels and odd pixels: dual-lvds-even-pixels and dual-lvds-odd-pixels,
> which means device drivers should not use bridge specific or panel
> specific dual_link flags. Also, in this case the DT describes the
> connection fully.
> 
> In order for the solution to be generic, I have exported a new helper
> (drm_of_lvds_get_dual_link_configuration) to walk the device tree,
> and figure out if the connection is dual-LVDS. The same helper gives
> information about the configuration of the connection. If Px is connected
> to a port expecting even pixels and Py is connected to a port expecting
> odd pixels, then the helper returns DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS
> (like in the example below), otherwise it returns
> DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS.
> 
> 
>  --------            dual-lvds-even-pixels  --------
> |        |----                         ----|        |
> |        | Px |---------------------->| Pn |        |
> |        |----                         ----|        |
> | SOURCE |           dual-lvds-odd-pixels  |  SINK  |
> |        |----                         ----|        |
> |        | Py |---------------------->| Pm |        |
> |        |----                         ----|        |
>  --------                                   --------
> 
> The device driver for the encoder then will work out if with the current
> wiring the pixels need swapping or not.
> 
> The same solution works for both panels and bridges.
> 
> Since the DT describes the connection fully, driver
> drivers/gpu/drm/panel/panel-lvds.c works out-of-the-box, no changes
> required, however, this implementation opens up a problem with the
> dt-bindings.
> Driver drivers/gpu/drm/panel/panel-lvds.c can still be pleased by
> a port node, but also by a ports node.
> I have created Documentation/devicetree/bindings/display/bus-timings/lvds.yaml
> with the idea of including it from panels and bridges dt-bindings
> supporting dual-LVDS (and of course the dt-bindings for the specific
> devices should say which port should be marked as what), but file
> Documentation/devicetree/bindings/display/panel/lvds.yaml formally
> requires property "port", while with this implementation it should require
> OneOf "port" and "ports", and unfortunately I can't seem to find a neat way
> aroud that, other than creating a new compatible string
> (e.g. "panel-dual-lvds"), a new dt-binding document for it, and of course adding
> support for the new compatible string to drivers/gpu/drm/panel/panel-lvds.c.
> As a result, this series is missing (at least) a patch necessary to fully
> document the new implementation within
> Documentation/devicetree/bindings/display/panel/lvds.yaml
> 
> Rob, do you have any suggestions? Do you think this idea works ok from a
> documentation point of view? By the way, I don't really know what I am doing
> with the yaml dt-bindings, I hope you won't be horrified by this series :-P
> 
> I hope I was able to deliver the concept clearly, if not please just ask.
> 
> Comments are very much appreciated.
> 
> Thanks,
> Fab
> 
> Fabrizio Castro (8):
>   dt-bindings: display: Add bindings for LVDS bus-timings
>   dt-bindings: display: Add idk-2121wr binding
>   drm: Add bus timings helper
>   drm: rcar-du: lvds: Add dual-LVDS panels support
>   drm: bridge: thc63: Do not report input bus mode through bridge
>     timings
>   arm64: dts: renesas: Add EK874 board with idk-2121wr display support
>   [HACK] arm64: dts: renesas: draak: Enable LVDS
>   [HACK] arm64: dts: renesas: draak: Enable LVDS dual-link operation
> 
>  .../bindings/display/bus-timings/lvds.yaml         |  38 +++++++
>  .../display/panel/advantech,idk-2121wr.yaml        |  90 ++++++++++++++++
>  arch/arm64/boot/dts/renesas/Makefile               |   3 +-
>  .../boot/dts/renesas/r8a774c0-ek874-idk-2121wr.dts | 116 +++++++++++++++++++++
>  arch/arm64/boot/dts/renesas/r8a77990-ebisu.dts     |  21 +++-
>  arch/arm64/boot/dts/renesas/r8a77995-draak.dts     |  26 +++--
>  drivers/gpu/drm/Makefile                           |   3 +-
>  drivers/gpu/drm/bridge/thc63lvd1024.c              |   9 +-
>  drivers/gpu/drm/drm_bus_timings.c                  |  97 +++++++++++++++++
>  drivers/gpu/drm/rcar-du/rcar_lvds.c                | 110 +++++++++++--------
>  include/drm/drm_bridge.h                           |   8 --
>  include/drm/drm_bus_timings.h                      |  21 ++++
>  12 files changed, 473 insertions(+), 69 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/display/bus-timings/lvds.yaml
>  create mode 100644 Documentation/devicetree/bindings/display/panel/advantech,idk-2121wr.yaml
>  create mode 100644 arch/arm64/boot/dts/renesas/r8a774c0-ek874-idk-2121wr.dts
>  create mode 100644 drivers/gpu/drm/drm_bus_timings.c
>  create mode 100644 include/drm/drm_bus_timings.h
> 
> --
> 2.7.4