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Message-ID: <8c6e790e-f1b6-46ab-9acf-bdea8076405b@linux.dev>
Date: Thu, 13 Feb 2025 18:03:28 +0530
From: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Thomas Zimmermann <tzimmermann@...e.de>, Maxime Ripard <mripard@...nel.org>,
David Airlie <airlied@...il.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Simona Vetter <simona@...ll.ch>, Nishanth Menon <nm@...com>,
Vignesh Raghavendra <vigneshr@...com>, Devarsh Thakkar <devarsht@...com>,
Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
Jayesh Choudhary <j-choudhary@...com>,
Francesco Dolcini <francesco@...cini.it>,
DRI Development List <dri-devel@...ts.freedesktop.org>,
Devicetree List <devicetree@...r.kernel.org>,
Linux Kernel List <linux-kernel@...r.kernel.org>,
Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>, Jyri Sarha <jyri.sarha@....fi>
Subject: Re: [PATCH v5 2/3] dt-bindings: display: ti: Add schema for AM625
OLDI Transmitter
Hi Tomi,
Thank you for reviewing the patches!
On 11/02/25 17:54, Tomi Valkeinen wrote:
> Hi,
>
> On 09/02/2025 18:09, 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>
>> ---
>> .../bindings/display/ti/ti,am625-oldi.yaml | 88 ++++++++++
>> .../bindings/display/ti/ti,am65x-dss.yaml | 154 ++++++++++++++++++
>> MAINTAINERS | 1 +
>> 3 files changed, 243 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/display/ti/
>> ti,am625-oldi.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/display/ti/ti,am625-
>> oldi.yaml b/Documentation/devicetree/bindings/display/ti/ti,am625-
>> oldi.yaml
>> new file mode 100644
>> index 000000000000..42a80a512660
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/display/ti/ti,am625-oldi.yaml
>> @@ -0,0 +1,88 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/display/ti/ti,am625-oldi.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Texas Instruments AM625 OLDI Transmitter
>> +
>> +maintainers:
>> + - Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> + - Aradhya Bhatia <aradhya.bhatia@...ux.dev>
>> +
>> +description:
>> + The AM625 TI Keystone OpenLDI transmitter (OLDI TX) supports
>> serialized RGB
>> + pixel data transmission between host and flat panel display over
>> LVDS (Low
>> + Voltage Differential Sampling) interface. The OLDI TX consists of
>> 7-to-1 data
>> + serializers, and 4-data and 1-clock LVDS outputs. It supports the
>> LVDS output
>> + formats "jeida-18", "jeida-24" and "vesa-18", and can accept 24-bit
>> RGB or
>> + padded and un-padded 18-bit RGB bus formats as input.
>> +
>> +properties:
>> + reg:
>> + maxItems: 1
>> +
>> + clocks:
>> + maxItems: 1
>> + description: serial clock input for the OLDI transmitters
>> +
>> + clock-names:
>> + const: serial
>> +
>> + ti,companion-oldi:
>> + $ref: /schemas/types.yaml#/definitions/phandle
>> + description:
>> + phandle to companion OLDI transmitter. This property is
>> mandatory for the
>> + primarty OLDI TX if the OLDI TXes are expected to work either
>> in dual-lvds
>> + mode or in clone mode. This property should point to the
>> secondary OLDI
>> + TX.
>> +
>> + ti,secondary-oldi:
>> + type: boolean
>> + description:
>> + Boolean property to mark the OLDI transmitter as the secondary
>> one, when the
>> + OLDI hardware is expected to run as a companion HW, in cases of
>> dual-lvds
>> + mode or clone mode. The primary OLDI hardware is responsible
>> for all the
>> + hardware configuration.
>
> I think these work, but I'm wondering if we would ever need to check
> something from the main oldi from the secondary oldi. In that case
> "crossed phandles" would be better, i.e. something like:
>
> (in the first oldi:)
> ti,slave-oldi = <phandle-to-second-oldi>
>
> (in the second oldi:)
> ti,master-oldi = <phandle-to-first-oldi>
When I had first designed the code and the devicetree for OLDI, it was
done so with the belief that we wouldn't reqiure a bridge instance for
the secondary OLDI, at all.
While that idea holds true for dual-lvds configuration, it doesn't so
for the clone mode configuration. For clone mode, as you pointed out, we
will require a 2nd bridge instance to configure any of the bridges and
panels that come after the 2nd OLDI.
>
> Then again, if we ever need that, even with these bindings the driver
> could find the first oldi, but needs to go via the dss's node.
While it is possible to do it this way, it might not be the cleanest
one. And _if_ there is a ever a DSS in future with more than 2 OLDI
TXes, say 4, then the decipher logic may get too complicated.
While I cannot think of any case where the secondary OLDI bridge DT
might need to access the primary OLDI bridge at the moment, I wonder if
we should play it safer and have this option anyway.
Maybe something like this?
(primary OLDI)
ti,primary-oldi;
ti,companion-oldi = <phandle-to-secondary-oldi>;
(secondary OLDI)
ti,secondary-oldi;
ti,companion-oldi = <phandle-to-primary-oldi>;
I will have to drop the condition below, and add ti,primary-oldi
property.
>
> So, just a thought.
>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>
>
>> + ti,oldi-io-ctrl:
>> + $ref: /schemas/types.yaml#/definitions/phandle
>> + description:
>> + phandle to syscon device node mapping OLDI IO_CTRL registers
>> found in the
>> + control MMR region. These registers are required to toggle the
>> I/O lane
>> + power, and control its electrical characteristics.
>> +
>> + ports:
>> + $ref: /schemas/graph.yaml#/properties/ports
>> +
>> + properties:
>> + port@0:
>> + $ref: /schemas/graph.yaml#/properties/port
>> + description: Parallel RGB input port
>> +
>> + port@1:
>> + $ref: /schemas/graph.yaml#/properties/port
>> + description: LVDS output port
>> +
>> + required:
>> + - port@0
>> + - port@1
>> +
>> +allOf:
>> + - if:
>> + required:
>> + - ti,secondary-oldi
>> + then:
>> + properties:
>> + ti,companion-oldi: false
>> +
(this condition)
>> +required:
>> + - reg
>> + - clocks
>> + - clock-names
>> + - ti,oldi-io-ctrl
>> + - ports
>> +
>> +additionalProperties: false
>> +
>> +...
>> diff --git a/Documentation/devicetree/bindings/display/ti/ti,am65x-
>> dss.yaml b/Documentation/devicetree/bindings/display/ti/ti,am65x-dss.yaml
>> index 399d68986326..a82c525631ea 100644
>> --- a/Documentation/devicetree/bindings/display/ti/ti,am65x-dss.yaml
>> +++ b/Documentation/devicetree/bindings/display/ti/ti,am65x-dss.yaml
>> @@ -91,6 +91,24 @@ properties:
>> For AM625 DSS, the internal DPI output port node from video
>> port 1.
>> For AM62A7 DSS, the port is tied off inside the SoC.
>> + properties:
>> + endpoint@0:
>> + $ref: /schemas/graph.yaml#/properties/endpoint
>> + description:
>> + For AM625 DSS, VP Connection to OLDI0.
>> + For AM65X DSS, OLDI output from the SoC.
>> +
>> + endpoint@1:
>> + $ref: /schemas/graph.yaml#/properties/endpoint
>> + description:
>> + For AM625 DSS, VP Connection to OLDI1.
>> +
>> + anyOf:
>> + - required:
>> + - endpoint
>> + - required:
>> + - endpoint@0
>> + - endpoint@1
>> port@1:
>> $ref: /schemas/graph.yaml#/properties/port
>> @@ -112,6 +130,25 @@ properties:
>> Input memory (from main memory to dispc) bandwidth limit in
>> bytes per second
>> + oldi-transmitters:
>> + description:
>> + Child node under the DSS, to describe all the OLDI transmitters
>> connected
>> + to the DSS videoports.
>> + type: object
>> + additionalProperties: false
>> +
>> + properties:
>> + "#address-cells":
>> + const: 1
>> +
>> + "#size-cells":
>> + const: 0
>> +
>> + patternProperties:
>> + '^oldi@[0-1]$':
>> + $ref: ti,am625-oldi.yaml#
>> + description: OLDI transmitters connected to the DSS VPs
>> +
>> allOf:
>> - if:
>> properties:
>> @@ -120,10 +157,25 @@ allOf:
>> const: ti,am62a7-dss
>> then:
>> properties:
>> + oldi-transmitters: false
>> ports:
>> properties:
>> port@0: false
>> + - if:
>> + properties:
>> + compatible:
>> + contains:
>> + const: ti,am65x-dss
>> + then:
>> + properties:
>> + oldi-transmitters: false
>> + ports:
>> + properties:
>> + port@0:
>> + properties:
>> + endpoint@1: false
>> +
>> required:
>> - compatible
>> - reg
>> @@ -171,3 +223,105 @@ examples:
>> };
>> };
>> };
>> +
>> + - |
>> + #include <dt-bindings/interrupt-controller/arm-gic.h>
>> + #include <dt-bindings/interrupt-controller/irq.h>
>> + #include <dt-bindings/soc/ti,sci_pm_domain.h>
>> +
>> + bus {
>> + #address-cells = <2>;
>> + #size-cells = <2>;
>> + dss1: dss@...00000 {
>> + compatible = "ti,am625-dss";
>> + reg = <0x00 0x30200000 0x00 0x1000>, /* common */
>> + <0x00 0x30202000 0x00 0x1000>, /* vidl1 */
>> + <0x00 0x30206000 0x00 0x1000>, /* vid */
>> + <0x00 0x30207000 0x00 0x1000>, /* ovr1 */
>> + <0x00 0x30208000 0x00 0x1000>, /* ovr2 */
>> + <0x00 0x3020a000 0x00 0x1000>, /* vp1 */
>> + <0x00 0x3020b000 0x00 0x1000>, /* vp2 */
>> + <0x00 0x30201000 0x00 0x1000>; /* common1 */
>> + reg-names = "common", "vidl1", "vid",
>> + "ovr1", "ovr2", "vp1", "vp2", "common1";
>> + power-domains = <&k3_pds 186 TI_SCI_PD_EXCLUSIVE>;
>> + clocks = <&k3_clks 186 6>,
>> + <&vp1_clock>,
>> + <&k3_clks 186 2>;
>> + clock-names = "fck", "vp1", "vp2";
>> + interrupts = <GIC_SPI 84 IRQ_TYPE_LEVEL_HIGH>;
>> + oldi-transmitters {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + oldi0: oldi@0 {
>> + reg = <0>;
>> + clocks = <&k3_clks 186 0>;
>> + clock-names = "serial";
>> + ti,companion-oldi = <&oldi1>;
>> + ti,oldi-io-ctrl = <&dss_oldi_io_ctrl>;
>> + ports {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + port@0 {
>> + reg = <0>;
>> + oldi0_in: endpoint {
>> + remote-endpoint = <&dpi0_out0>;
>> + };
>> + };
>> + port@1 {
>> + reg = <1>;
>> + oldi0_out: endpoint {
>> + remote-endpoint = <&panel_in0>;
>> + };
>> + };
>> + };
>> + };
>> + oldi1: oldi@1 {
>> + reg = <1>;
>> + clocks = <&k3_clks 186 0>;
>> + clock-names = "serial";
>> + ti,secondary-oldi;
>> + ti,oldi-io-ctrl = <&dss_oldi_io_ctrl>;
>> + ports {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + port@0 {
>> + reg = <0>;
>> + oldi1_in: endpoint {
>> + remote-endpoint = <&dpi0_out1>;
>> + };
>> + };
>> + port@1 {
>> + reg = <1>;
>> + oldi1_out: endpoint {
>> + remote-endpoint = <&panel_in1>;
>> + };
>> + };
>> + };
>> + };
>> + };
>> + ports {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + port@0 {
>> + #address-cells = <1>;
>> + #size-cells = <0>;
>> + reg = <0>;
>> + dpi0_out0: endpoint@0 {
>> + reg = <0>;
>> + remote-endpoint = <&oldi0_in>;
>> + };
>> + dpi0_out1: endpoint@1 {
>> + reg = <1>;
>> + remote-endpoint = <&oldi1_in>;
>> + };
>> + };
>> + port@1 {
>> + reg = <1>;
>> + dpi1_out: endpoint {
>> + remote-endpoint = <&hdmi_bridge>;
>> + };
>> + };
>> + };
>> + };
>> + };
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 0fa7c5728f1e..88fa2d9435b8 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -7816,6 +7816,7 @@ M: Tomi Valkeinen
>> <tomi.valkeinen@...asonboard.com>
>> L: dri-devel@...ts.freedesktop.org
>> S: Maintained
>> T: git https://gitlab.freedesktop.org/drm/misc/kernel.git
>> +F: Documentation/devicetree/bindings/display/ti/ti,am625-oldi.yaml
>> F: Documentation/devicetree/bindings/display/ti/ti,am65x-dss.yaml
>> F: Documentation/devicetree/bindings/display/ti/ti,j721e-dss.yaml
>> F: Documentation/devicetree/bindings/display/ti/ti,k2g-dss.yaml
>
--
Regards
Aradhya
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