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SubjectRe: [PATCH v2 0/3] drm: Add LVDS decoder bridge
From
Date
Hi,

On Friday 09 March 2018 07:21 PM, 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()".

I think this is the way to go. DRM doesn't say anywhere that we can't
have 2 drm_bridge-s contained in a single device. About the issue with
of_drm_find_bridge(), if you set the 2 bridge's 'of_node' field to
the bridge1 and bridge2 nodes as shown below, wouldn't that suffice.
From what I know, we don't necessarily need to set the bridge's of_node
to the device (i.e, thschip) itself.

thschip {
...
ports {
bridge1: port@0 {
...
};

bridge2: port@1 {
...
};
};
};


Thanks,
Archit

> 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
>

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