linux-kernel - [PATCH v2 0/3] drm: Add LVDS decoder bridge

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Date:   Fri,  9 Mar 2018 14:51:37 +0100
From:   Jacopo Mondi <jacopo+renesas@...ndi.org>
To:     architt@...eaurora.org, a.hajda@...sung.com,
        Laurent.pinchart@...asonboard.com, airlied@...ux.ie,
        horms@...ge.net.au, magnus.damm@...il.com, geert@...ux-m68k.org,
        niklas.soderlund@...natech.se, sergei.shtylyov@...entembedded.com,
        robh+dt@...nel.org, mark.rutland@....com
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/3] drm: Add LVDS decoder bridge

Hello,
   after some discussion on the proposed bindings for generic lvds decoder and
Thine THC63LVD1024, I decided to drop the THC63 specific part and just live with
a transparent decoder that does not support any configuration from DT.

Dropping THC63 support to avoid discussion on how to better implement support
for a DRM bridge with 2 input ports and focus on LVDS mode propagation through
bridges as explained in v1 cover letter (for DRM people: please see [1] as why
I find difficult to implement support for bridges with multiple input endpoints)

Same base branch as v1, with same patches for V3M Eagle applied on top.
git://jmondi.org/linux v3m/v4.16-rc3/base

Thanks
   j

v1 -> v2:
- Drop support for THC63LVD1024

[1] I had a quick at how to model a DRM bridge with multiple input
ports, and I see a blocker in how DRM identifies and matches bridges using
the devices node in place of the endpoint nodes.

As THC63LVD1024 supports up to 2 LVDS inputs and 2 LVDS outputs, I see only
a few ways to support that:
 1) register 2 drm bridges from the same driver (one for each input/output pair)
    but they would both be matches on the same device node when the preceding
    bridge calls "of_drm_find_bridge()".
 2) register a single bridge with multiple "next bridges", but when the bridge
    gets attached I don't see a way on how to identify on which next bridge
    "drm_bridge_attach()" on, as it depends on the endpoint the current bridge
    has been attached on first, and we don't have that information.
 3) Register more instances of the same chip in DTS, one for each input/output
    pair. They gonna share supplies and gpios, and I don't like that.

I had a quick look at the currently in mainline bridges and none of them has
multiple input endpoints, except for HDMI audio endpoint, which I haven't found
in use in any DTS. I guess the problem has been already debated and maybe solved
in the past, so feel free to point me to other sources.

Jacopo Mondi (3):
  dt-bindings: display: bridge: Document LVDS to parallel decoder
  drm: bridge: Add LVDS decoder driver
  arm64: dts: renesas: Add LVDS decoder to R-Car V3M Eagle

 .../bindings/display/bridge/lvds-decoder.txt       |  42 ++++++
 arch/arm64/boot/dts/renesas/r8a77970-eagle.dts     |  31 +++-
 drivers/gpu/drm/bridge/Kconfig                     |   8 ++
 drivers/gpu/drm/bridge/Makefile                    |   1 +
 drivers/gpu/drm/bridge/lvds-decoder.c              | 157 +++++++++++++++++++++
 5 files changed, 237 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/lvds-decoder.txt
 create mode 100644 drivers/gpu/drm/bridge/lvds-decoder.c

--
2.7.4