linux-kernel - Re: [PATCH v9 2/4] dt-bindings: display: ti: Add schema for AM625 OLDI Transmitter

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Message-ID: <174913450088.2539370.15860584421984514366.robh@kernel.org>
Date: Thu, 5 Jun 2025 09:41:44 -0500
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: Devarsh Thakkar <devarsht@...com>,
	Alexander Sverdlin <alexander.sverdlin@...mens.com>,
	Devicetree List <devicetree@...r.kernel.org>,
	Simona Vetter <simona@...ll.ch>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Maxime Ripard <mripard@...nel.org>,
	Michael Walle <mwalle@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Jyri Sarha <jyri.sarha@....fi>,
	Vignesh Raghavendra <vigneshr@...com>,
	Conor Dooley <conor+dt@...nel.org>,
	Francesco Dolcini <francesco@...cini.it>,
	David Airlie <airlied@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Jayesh Choudhary <j-choudhary@...com>, Nishanth Menon <nm@...com>,
	DRI Development List <dri-devel@...ts.freedesktop.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>
Subject: Re: [PATCH v9 2/4] dt-bindings: display: ti: Add schema for AM625
 OLDI Transmitter


On Wed, 28 May 2025 17:55:42 +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@...com>
> 
> The OLDI transmitters (TXes) do not have registers of their own, and are
> dependent on the source video-ports (VPs) from the DSS to provide
> configuration data. This hardware doesn't directly sit on the internal
> bus of the SoC, but does so via the DSS. Hence, the OLDI TXes are
> supposed to be child nodes under the DSS, and not independent devices.
> 
> Two of the OLDI TXes can function in tandem to output dual-link OLDI
> output, or cloned single-link outputs. In these cases, one OLDI will be
> the primary OLDI, and the other one, a companion. The following diagram
> represents such a configuration.
> 
> +-----+-----+         +-------+
> |     |     |         |       |
> |     | VP1 +----+--->+ OLDI0 |  (Primary - may need companion)
> |     |     |    |    |       |
> | DSS +-----+    |    +-------+
> |     |     |    |
> |     | VP2 |    |    +-------+
> |     |     |    |    |       |
> +-----+-----+    +--->+ OLDI1 |  (Companion OLDI)
>                       |       |
>                       +-------+
> 
> The DSS in AM625 SoC has a configuration like the one above. The AM625
> DSS VP1 (port@0) can connect and control 2 OLDI TXes, to use them in
> dual-link or cloned single-link OLDI modes. It is only the VP1 that can
> connect to either OLDI TXes for the AM625 DSS, and not the VP2.
> 
> Alternatively, on some future TI SoCs, along with the above
> configuration, the OLDI TX can _also_ connect to separate video sources,
> making them work entirely independent of each other. In this case,
> neither of the OLDIs are "companion" or "secondary" OLDIs, and nor do
> they require one. They both are independent and primary OLDIs. The
> following diagram represents such a configuration.
> 
> +-----+-----+               +-------+
> |     |     |               |       |
> |     | VP1 +--+----------->+ OLDI0 |  (Primary - may need companion)
> |     |     |  |            |       |
> |     +-----+  |            +-------+
> |     |     |  |
> |     | VP2 |  |
> |     |     |  |
> | DSS +-----+  |   +---+    +-------+
> |     |     |  +-->+ M |    |       |
> |     | VP3 +----->+ U +--->+ OLDI1 |  (Companion or Primary)
> |     |     |      | X |    |       |
> |     +-----+      +---+    +-------+
> |     |     |
> |     | VP4 |
> |     |     |
> +-----+-----+
> 
> Note that depending on the mux configuration, the OLDIs can either be
> working together in tandem - sourced by VP1, OR, they could be working
> independently sourced by VP1 and VP3 respectively.
> The idea is to support all the configurations with this OLDI TX schema.
> 
> The OLDI functionality is further supported by a system-control module,
> which contains a few registers to control OLDI IO power and other
> electrical characteristics of the IO lanes.
> 
> Add devicetree binding schema for the OLDI TXes to support various
> configurations, and extend their support to the AM625 DSS.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
> ---
> Changes Log:
> V9:
>   - Reword the "ti,companion-oldi" property description.
>   - Fix the missing "ti,companion-oldi" property in the schema example.
>   - v8 of this patch: https://lore.kernel.org/all/20250525151721.567042-3-aradhya.bhatia@linux.dev/
> 
> V8:
>   - Drop the condition that made the "secondary-oldi" and "companion-oldi"
>     properties mutually exclusive.
>   - Add "ti,am62l-dss" compatible to the list of compatibles that cannot
>     use the multiple endpoints or have "oldi-transmitters", on port@0.
>   - Because of above, drop R-b tags from Tomi Valkeinen, and Rob Herring.
>   - v7 of this patch: https://lore.kernel.org/all/20250329133943.110698-3-aradhya.bhatia@linux.dev/
> 
> ---
>  .../bindings/display/ti/ti,am625-oldi.yaml    |  79 +++++++++
>  .../bindings/display/ti/ti,am65x-dss.yaml     | 157 ++++++++++++++++++
>  MAINTAINERS                                   |   1 +
>  3 files changed, 237 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/ti/ti,am625-oldi.yaml
> 

Reviewed-by: Rob Herring (Arm) <robh@...nel.org>