Re: [PATCH v1 3/6] dt-bindings: display: tegra: Document 8-bit CPU parallel interface
From: Mikko Perttunen
Date: Fri Oct 02 2026 - 01:58:32 EST
On Thursday, October 1, 2026 3:03 AM Svyatoslav Ryhel wrote:
> ср, 30 вер. 2026 р. о 12:19 Mikko Perttunen <mperttunen@xxxxxxxxxx> пише:
> >
> > On Wednesday, September 30, 2026 4:05 PM Svyatoslav Ryhel wrote:
> > > Document 8-bit CPU parallel MIPI DBI Type B interface provided by
> > > Tegra20/30 SoCs display controller.
> > >
> > > Signed-off-by: Svyatoslav Ryhel <clamor95@xxxxxxxxx>
> > > ---
> > > .../display/tegra/nvidia,tegra-8bit-cpu.yaml | 138 ++++++++++++++++++
> > > 1 file changed, 138 insertions(+)
> > > create mode 100644 Documentation/devicetree/bindings/display/tegra/nvidia,tegra-8bit-cpu.yaml
> > >
> > > diff --git a/Documentation/devicetree/bindings/display/tegra/nvidia,tegra-8bit-cpu.yaml b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra-8bit-cpu.yaml
> > > new file mode 100644
> > > index 0000000000000..f0dab608b2936
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra-8bit-cpu.yaml
> > > @@ -0,0 +1,138 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/display/tegra/nvidia,tegra-8bit-cpu.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Nvidia Tegra DC based MIPI DBI Type B bridge
> > > +
> > > +maintainers:
> > > + - Svyatoslav Ryhel <clamor95@xxxxxxxxx>
> > > +
> > > +description: The display controller in Tegra20/30 SoCs features an
> > > + 8-bit SPI interface that closely resembles the MIPI DBI Type B
> > > + protocol and is referred to as '8-bit CPU'. Each display controller
> > > + provides two such interfaces, which can be used to send MIPI DCS
> > > + commands to initialize and control the panel while image data is
> > > + transmitted via 16/18/24-line RGB.
> > > +
> > > +properties:
> > > + compatible:
> > > + const: nvidia,tegra-8bit-cpu
> > > +
> > > + dc-gpios:
> > > + description: Data/command selection pin.
> > > + maxItems: 1
> > > +
> > > + rw-gpios:
> > > + description: Read/write pin.
> > > + maxItems: 1
> > > +
> > > + cs-gpios:
> > > + description: Chip select pin.
> > > + maxItems: 1
> > > +
> > > + data-gpios:
> > > + description: Specifies a set of 8 gpio pins used to transfer data.
> > > + minItems: 8
> > > + maxItems: 8
> >
> > Based on my admittedly brief research, according to the TRM the display
> > controller can drive all of these pins - of which there are two fixed
> > sets as you mention - directly. So we'd need to describe which interface
> > the display is connected to in DT, but not any GPIOs (which they really
> > aren't).
> >
>
> Thierry, Mikko.
>
> I am not sure how to approach GPIOs defined outside of Device Tree.
> All GPIO interactions are done either by ofnode/fwnode or software
> nodes. Global gpio declaration is in process of being removed and
> legacy GPIO API seem to be not long-therm sustainable. How to resolve
> this? Should I keep above layout with GPIOs defined in the tree?
I looked a bit closer and I now think the initialization sequences
cannot be done entirely through the display controller - so this is
correct, we do need the GPIO stuff.
>
> > > +
> > > + nvidia,init-sequence:
> > > + $ref: /schemas/types.yaml#/definitions/uint32-array
> > > + description: Device specific set of values used in DC DISP_SPI_INIT_SEQ
> > > + registers.
> > > + minItems: 4
> > > + maxItems: 4
> >
> > And AIUI this is panel-specific DBI commands the display controller will
> > transmit. So ideally the display driver should receive this data from
> > the panel driver.
> >
> > Thank you
> > Mikko
> >
> > > +
> > > + panel:
> > > + type: object
> > > + description: Node of supported panel driven by the bridge.
> > > +
> > > + ports:
> > > + $ref: /schemas/graph.yaml#/properties/ports
> > > +
> > > + properties:
> > > + port@0:
> > > + $ref: /schemas/graph.yaml#/$defs/port-base
> > > + unevaluatedProperties: false
> > > + description: Video port for RGB input.
> > > +
> > > + properties:
> > > + endpoint:
> > > + $ref: /schemas/graph.yaml#/$defs/endpoint-base
> > > + unevaluatedProperties: false
> > > +
> > > + properties:
> > > + bus-width:
> > > + enum: [ 16, 18, 24 ]
> > > +
> > > + port@1:
> > > + $ref: /schemas/graph.yaml#/properties/port
> > > + description: Video port for DBI output (panel or connector).
> > > +
> > > + required:
> > > + - port@0
> > > + - port@1
> > > +
> > > +required:
> > > + - compatible
> > > + - ports
> > > +
> > > +unevaluatedProperties: false
> > > +
> > > +examples:
> > > + - |
> > > + #include <dt-bindings/gpio/gpio.h>
> > > +
> > > + dbi-bridge {
> > > + compatible = "nvidia,tegra-8bit-cpu";
> > > +
> > > + dc-gpios = <&gpio 110 GPIO_ACTIVE_HIGH>;
> > > + rw-gpios = <&gpio 11 GPIO_ACTIVE_HIGH>;
> > > + cs-gpios = <&gpio 108 GPIO_ACTIVE_HIGH>;
> > > +
> > > + data-gpios = <&gpio 32 GPIO_ACTIVE_HIGH>, <&gpio 33 GPIO_ACTIVE_HIGH>,
> > > + <&gpio 34 GPIO_ACTIVE_HIGH>, <&gpio 35 GPIO_ACTIVE_HIGH>,
> > > + <&gpio 36 GPIO_ACTIVE_HIGH>, <&gpio 37 GPIO_ACTIVE_HIGH>,
> > > + <&gpio 38 GPIO_ACTIVE_HIGH>, <&gpio 39 GPIO_ACTIVE_HIGH>;
> > > +
> > > + nvidia,init-sequence = <0x0000002c 0x0 0x0 0x00005000>;
> > > +
> > > + panel {
> > > + compatible = "hit,tx10d07vm0baa";
> > > +
> > > + reset-gpios = <&gpio 175 GPIO_ACTIVE_LOW>;
> > > +
> > > + avci-supply = <&vcc_2v8_lcd>;
> > > + iovcc-supply = <&iovcc_1v8_lcd>;
> > > +
> > > + backlight = <&backlight>;
> > > +
> > > + port {
> > > + panel_input: endpoint {
> > > + remote-endpoint = <&bridge_output>;
> > > + };
> > > + };
> > > + };
> > > +
> > > + ports {
> > > + #address-cells = <1>;
> > > + #size-cells = <0>;
> > > +
> > > + port@0 {
> > > + reg = <0>;
> > > +
> > > + bridge_input: endpoint {
> > > + remote-endpoint = <&dpi_output>;
> > > + };
> > > + };
> > > +
> > > + port@1 {
> > > + reg = <1>;
> > > +
> > > + bridge_output: endpoint {
> > > + remote-endpoint = <&panel_input>;
> > > + };
> > > + };
> > > + };
> > > + };
> > > --
> > > 2.53.0
> > >
> > >
> >
> >
> >
> >