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    SubjectRe: [PATCH v2 0/3] drm: Add LVDS decoder bridge
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    On 09.03.2018 14:51, Jacopo Mondi wrote:
    > 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.

    I think this is is a step in wrong direction, IMHO. Your previous
    patchset was quite OK, at least bindings, IMHO. Few things needed only
    polishing.
    Here we have unmanaged/transparent bridge, which is totally different,
    what happened to regulators and gpios from previous iteration.
    I do not have schematics of the board, but I guess respective pins of
    the bridge must be connected somehow.
    I think the problem you want to avoid (double bridge) should not be a
    problem at all.
    I suppose the most important is to have correct bindings - as they need
    to be stable.
    If you really must to do hacks better is to put them into driver.

    Regards
    Andrzej

    >
    > 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
    >
    >
    >
    >

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