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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
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+MIPI DSI (Display Serial Interface) busses
+==========================================
+
+The MIPI Display Serial Interface specifies a serial bus and a protocol for
+communication between a host and up to four peripherals. This document will
+define the syntax used to represent a DSI bus in a device tree.
+
+This document describes DSI bus-specific properties only or defines existing
+standard properties in the context of the DSI bus.
+
+Each DSI host provides a DSI bus. The DSI host controller's node contains a
+set of properties that characterize the bus. Child nodes describe individual
+peripherals on that bus.
+
+The following assumes that only a single peripheral is connected to a DSI
+host. Experience shows that this is true for the large majority of setups.
+
+DSI host
+========
+
+In addition to the standard properties and those defined by the parent bus of
+a DSI host, the following properties apply to a node representing a DSI host.
+
+Required properties:
+- #address-cells: The number of cells required to represent an address on the
+ bus. DSI peripherals are addressed using a 2-bit virtual channel number, so
+ a maximum of 4 devices can be addressed on a single bus. Hence the value of
+ this property should be 1.
+- #size-cells: Should be 0. There are cases where it makes sense to use a
+ different value here. See below.
+
+Optional properties:
+- clock-master: boolean. Should be enabled if the host is being used in
+ conjunction with another DSI host to drive the same peripheral. Hardware
+ supporting such a configuration generally requires the data on both the busses
+ to be driven by the same clock. Only the DSI host instance controlling this
+ clock should contain this property.
+
+DSI peripheral
+==============
+
+Peripherals with DSI as control bus, or no control bus
+------------------------------------------------------
+
+Peripherals with the DSI bus as the primary control bus, or peripherals with
+no control bus but use the DSI bus to transmit pixel data are represented
+as child nodes of the DSI host's node. Properties described here apply to all
+DSI peripherals, but individual bindings may want to define additional,
+device-specific properties.
+
+Required properties:
+- reg: The virtual channel number of a DSI peripheral. Must be in the range
+ from 0 to 3.
+
+Some DSI peripherals respond to more than a single virtual channel. In that
+case two alternative representations can be chosen:
+- The reg property can take multiple entries, one for each virtual channel
+ that the peripheral responds to.
+- If the virtual channels that a peripheral responds to are consecutive, the
+ #size-cells can be set to 1. The first cell of each entry in the reg
+ property is the number of the first virtual channel and the second cell is
+ the number of consecutive virtual channels.
+
+Peripherals with a different control bus
+----------------------------------------
+
+There are peripherals that have I2C/SPI (or some other non-DSI bus) as the
+primary control bus, but are also connected to a DSI bus (mostly for the data
+path). Connections between such peripherals and a DSI host can be represented
+using the graph bindings [1], [2].
+
+Peripherals that support dual channel DSI
+-----------------------------------------
+
+Peripherals with higher bandwidth requirements can be connected to 2 DSI
+busses. Each DSI bus/channel drives some portion of the pixel data (generally
+left/right half of each line of the display, or even/odd lines of the display).
+The graph bindings should be used to represent the multiple DSI busses that are
+connected to this peripheral. Each DSI host's output endpoint can be linked to
+an input endpoint of the DSI peripheral.
+
+[1] Documentation/devicetree/bindings/graph.txt
+[2] Documentation/devicetree/bindings/media/video-interfaces.txt
+
+Examples
+========
+- (1), (2) and (3) are examples of a DSI host and peripheral on the DSI bus
+ with different virtual channel configurations.
+- (4) is an example of a peripheral on a I2C control bus connected to a
+ DSI host using of-graph bindings.
+- (5) is an example of 2 DSI hosts driving a dual-channel DSI peripheral,
+ which uses I2C as its primary control bus.
+
+1)
+ dsi-host {
+ ...
+
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ /* peripheral responds to virtual channel 0 */
+ peripheral@0 {
+ compatible = "...";
+ reg = <0>;
+ };
+
+ ...
+ };
+
+2)
+ dsi-host {
+ ...
+
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ /* peripheral responds to virtual channels 0 and 2 */
+ peripheral@0 {
+ compatible = "...";
+ reg = <0, 2>;
+ };
+
+ ...
+ };
+
+3)
+ dsi-host {
+ ...
+
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ /* peripheral responds to virtual channels 1, 2 and 3 */
+ peripheral@1 {
+ compatible = "...";
+ reg = <1 3>;
+ };
+
+ ...
+ };
+
+4)
+ i2c-host {
+ ...
+
+ dsi-bridge@35 {
+ compatible = "...";
+ reg = <0x35>;
+
+ ports {
+ ...
+
+ port {
+ bridge_mipi_in: endpoint {
+ remote-endpoint = <&host_mipi_out>;
+ };
+ };
+ };
+ };
+ };
+
+ dsi-host {
+ ...
+
+ ports {
+ ...
+
+ port {
+ host_mipi_out: endpoint {
+ remote-endpoint = <&bridge_mipi_in>;
+ };
+ };
+ };
+ };
+
+5)
+ i2c-host {
+ dsi-bridge@35 {
+ compatible = "...";
+ reg = <0x35>;
+
+ ports {
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ port@0 {
+ reg = <0>;
+ dsi0_in: endpoint {
+ remote-endpoint = <&dsi0_out>;
+ };
+ };
+
+ port@1 {
+ reg = <1>;
+ dsi1_in: endpoint {
+ remote-endpoint = <&dsi1_out>;
+ };
+ };
+ };
+ };
+ };
+
+ dsi0-host {
+ ...
+
+ /*
+ * this DSI instance drives the clock for both the host
+ * controllers
+ */
+ clock-master;
+
+ ports {
+ ...
+
+ port {
+ dsi0_out: endpoint {
+ remote-endpoint = <&dsi0_in>;
+ };
+ };
+ };
+ };
+
+ dsi1-host {
+ ...
+
+ ports {
+ ...
+
+ port {
+ dsi1_out: endpoint {
+ remote-endpoint = <&dsi1_in>;
+ };
+ };
+ };
+ };