Re: [PATCH v2 01/23] dt-bindings: display: msm: Add Qualcomm DCP

[Dmitry Baryshkov]

On Mon, Oct 26, 2026 at 11:51:11AM +0530, Jayant Shekhar wrote:
> DCP platforms place the display pipeline under firmware control, so Linux
> cannot discover display resources through direct register access. The DRM
> driver therefore needs device-tree descriptions of the Qualcomm transport
> wrapper, display topology, IOMMU contexts, and panel connections.
> 
> Add bindings for the Qualcomm DCP transport wrapper and VirtIO display
> subsystem. Document the IPCC power-notify resources, transport and
> framebuffer IOMMU contexts, firmware-visible IOVA range, INTF graph, and
> DSI panel connections. The wrapper creates a standard VirtIO-MMIO child
> after the IPCC power-notify sequence has completed.
> 
> Assisted-by: LLM
> Signed-off-by: Jayant Shekhar <jayant.shekhar@xxxxxxxxxxxxxxxx>
> ---
>  .../bindings/display/msm/qcom,dcp-dsi.yaml         |  79 ++++++++++++
>  .../devicetree/bindings/display/msm/qcom,dcp.yaml  | 123 +++++++++++++++++++
>  .../bindings/virtio/qcom,dcp-virtio.yaml           | 132 +++++++++++++++++++++
>  3 files changed, 334 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/msm/qcom,dcp-dsi.yaml b/Documentation/devicetree/bindings/display/msm/qcom,dcp-dsi.yaml
> new file mode 100644
> index 000000000000..9a0acaf00bb3
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/msm/qcom,dcp-dsi.yaml
> @@ -0,0 +1,79 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/msm/qcom,dcp-dsi.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Qualcomm DCP DSI host
> +
> +maintainers:
> +  - Jayant Shekhar <jayant.shekhar@xxxxxxxxxxxxxxxx>
> +
> +description: |
> +  A MIPI DSI host exposed by the Qualcomm DCP VirtIO device (see
> +  qcom,dcp.yaml). It follows the generic DSI controller binding, with panel
> +  devices described as child nodes. The DCP INTF graph endpoint connects
> +  directly to the panel; the DSI host node is not a graph endpoint. The host
> +  node uses the dsi@N naming convention, and its reg property identifies the
> +  DSI host index.
> +
> +allOf:
> +  - $ref: /schemas/display/dsi-controller.yaml#

If there are no separate compatibles, can this be folded into the main
DCP schema?

> +
> +properties:
> +  reg:
> +    maxItems: 1
> +    description: DSI host index matching the DCP output port.
> +
> +required:
> +  - reg
> +  - "#address-cells"
> +  - "#size-cells"
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    dcp-subsystem {
> +        compatible = "virtio,device34";
> +        iommus = <&apps_smmu 0x400 0x2>;
> +
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        ports {
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            port@0 {
> +                reg = <0>;
> +                dcp_intf0_out: endpoint {
> +                    remote-endpoint = <&panel_dcp_in>;
> +                };
> +            };
> +        };
> +
> +        dsi@0 {
> +            reg = <0>;
> +            #address-cells = <1>;
> +            #size-cells = <0>;

Yes, fold it there. It's not a separate device on its own.

> +
> +            panel@0 {
> +                compatible = "novatek,nt37801";
> +                reg = <0>;
> +
> +                vddio-supply = <&vreg_l12b_1p8>;
> +                vci-supply = <&vreg_l13b_3p0>;
> +                vdd-supply = <&display_panel_vdd>;
> +                reset-gpios = <&tlmm 210 GPIO_ACTIVE_LOW>;
> +
> +                port {
> +                    panel_dcp_in: endpoint {
> +                        remote-endpoint = <&dcp_intf0_out>;
> +                    };
> +                };
> +            };
> +        };
> +    };
> diff --git a/Documentation/devicetree/bindings/display/msm/qcom,dcp.yaml b/Documentation/devicetree/bindings/display/msm/qcom,dcp.yaml
> new file mode 100644
> index 000000000000..96f6c2a17e9e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/msm/qcom,dcp.yaml
> @@ -0,0 +1,123 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/msm/qcom,dcp.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Qualcomm Display Co-Processor (DCP)
> +
> +maintainers:
> +  - Jayant Shekhar <jayant.shekhar@xxxxxxxxxxxxxxxx>
> +
> +description: |
> +  The Display Co-Processor (DCP) is a firmware-owned display subsystem.
> +  Linux communicates with DCP over HFI through VirtIO and does not access
> +  display hardware registers directly.
> +
> +  This node describes the externally connected display graph between DCP
> +  INTF outputs and attached DSI panels. It is assigned to the VirtIO device
> +  by the Qualcomm transport driver and is not independently enumerated.
> +  Firmware capabilities and internal resources, including pipes, mixers,
> +  CRTCs, and clocks, are discovered at runtime.
> +
> +allOf:
> +  - $ref: /schemas/virtio/virtio-device.yaml#
> +
> +properties:
> +  compatible:
> +    const: virtio,device34
> +
> +  iommus:
> +    maxItems: 1
> +    description:
> +      SMMU context used by DCP firmware to access GEM framebuffers. This
> +      is separate from the HFI transport context specified by the
> +      iommus property on the parent DCP transport node.
> +      The child context is used for framebuffer DMA performed by DCP
> +      firmware, while the parent context is used for VirtIO transport and HFI
> +      queue buffers. These contexts represent distinct firmware-visible DMA
> +      address spaces and must not be used interchangeably.
> +
> +  "#address-cells":
> +    const: 1
> +
> +  "#size-cells":
> +    const: 0
> +
> +  ports:
> +    $ref: /schemas/graph.yaml#/properties/ports
> +    description: |
> +      DPU INTF output-only ports. The port number matches the firmware INTF
> +      index. The corresponding DSI host is the child node whose reg value
> +      matches the port number; the graph endpoint itself connects directly to
> +      the attached panel. Unused INTF ports are omitted.
> +    unevaluatedProperties: false
> +    patternProperties:
> +      "^port@[0-9a-f]+$":
> +        $ref: /schemas/graph.yaml#/$defs/port-base
> +        unevaluatedProperties: false
> +        properties:
> +          endpoint:
> +            $ref: /schemas/graph.yaml#/$defs/endpoint-base
> +            unevaluatedProperties: false
> +            required:
> +              - remote-endpoint
> +
> +patternProperties:
> +  "^dsi@[0-9a-f]+$":
> +    $ref: qcom,dcp-dsi.yaml#

When adding DP support, would you add more devices at the same level? If
so, we risk getting a warning about multiple devices using the same
address.

> +required:
> +  - compatible
> +  - iommus
> +  - "#address-cells"
> +  - "#size-cells"
> +  - ports
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    dcp-subsystem {
> +        compatible = "virtio,device34";
> +        iommus = <&apps_smmu 0x400 0x2>;
> +
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        ports {
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            port@0 {
> +                reg = <0>;
> +                dcp_intf0_out: endpoint {
> +                    remote-endpoint = <&panel_dcp_in>;
> +                };
> +            };
> +        };
> +
> +        dsi@0 {
> +            reg = <0>;
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            panel@0 {
> +                compatible = "novatek,nt37801";
> +                reg = <0>;
> +
> +                vddio-supply = <&vreg_l12b_1p8>;
> +                vci-supply = <&vreg_l13b_3p0>;
> +                vdd-supply = <&display_panel_vdd>;
> +                reset-gpios = <&tlmm 210 GPIO_ACTIVE_LOW>;
> +
> +                port {
> +                    panel_dcp_in: endpoint {
> +                        remote-endpoint = <&dcp_intf0_out>;
> +                    };
> +                };
> +            };
> +        };
> +    };
> diff --git a/Documentation/devicetree/bindings/virtio/qcom,dcp-virtio.yaml b/Documentation/devicetree/bindings/virtio/qcom,dcp-virtio.yaml
> new file mode 100644
> index 000000000000..6020e848ce25
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/virtio/qcom,dcp-virtio.yaml
> @@ -0,0 +1,132 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/virtio/qcom,dcp-virtio.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Qualcomm DCP VirtIO transport
> +
> +maintainers:
> +  - Jayant Shekhar <jayant.shekhar@xxxxxxxxxxxxxxxx>
> +
> +description: |
> +  Qualcomm DCP VirtIO transport. The IPCC power-notify channel and
> +  associated interrupts are required before the transport can access its
> +  MMIO registers. This is a Qualcomm-specific transport and must not use the
> +  generic virtio-mmio driver. The DCP VirtIO function is described as a child
> +  node and is assigned to the registered VirtIO device by this transport.
> +
> +properties:
> +  compatible:
> +    const: qcom,dcp-virtio
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts-extended:
> +    minItems: 2
> +    maxItems: 2
> +    description: The VirtIO-MMIO and DCP power-notify interrupts, in that order.
> +
> +  iommus:
> +    maxItems: 1
> +
> +  iommu-ranges:
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    description: |
> +      The firmware-visible IOVA range, specified as a four-cell tuple
> +      containing a 64-bit IOVA base followed by a 64-bit range size.
> +    items:
> +      - description: IOVA base, high cell
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +      - description: IOVA base, low cell
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +      - description: IOVA range size, high cell
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +      - description: IOVA range size, low cell
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +
> +  dma-coherent: true
> +
> +  mboxes:
> +    maxItems: 1
> +
> +  mbox-names:
> +    const: dcp-power-tx
> +
> +  dcp-subsystem:

'dcp' is not a generic name. If you want to list it here, it should be
something like 'display-subsystem' or 'display-controller'.

> +    $ref: ../display/msm/qcom,dcp.yaml#
> +
> +required:
> +  - compatible
> +  - reg
> +  - interrupts-extended
> +  - iommus
> +  - iommu-ranges
> +  - dma-coherent
> +  - mboxes
> +  - mbox-names
> +  - dcp-subsystem
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> +    #include <dt-bindings/interrupt-controller/irq.h>
> +    #include <dt-bindings/mailbox/qcom-ipcc.h>
> +
> +    virtio@9be8000 {
> +        compatible = "qcom,dcp-virtio";
> +        reg = <0x09be8000 0x1000>;
> +        interrupts-extended = <&intc GIC_ESPI 956 IRQ_TYPE_LEVEL_HIGH>,
> +                              <&ipcc 13 5 IRQ_TYPE_EDGE_RISING>;
> +        iommus = <&apps_smmu 0x15a3 0x0>;
> +        iommu-ranges = <0x0 0x84000000 0x0 0x04000000>;

This doesn't match the address / size cells.

> +        dma-coherent;
> +        mboxes = <&ipcc 13 5>;
> +        mbox-names = "dcp-power-tx";
> +
> +        dcp-subsystem {
> +            compatible = "virtio,device34";
> +            iommus = <&apps_smmu 0x400 0x2>;
> +
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            ports {
> +                #address-cells = <1>;
> +                #size-cells = <0>;
> +
> +                port@0 {
> +                    reg = <0>;
> +                    dcp_intf0_out: endpoint {
> +                        remote-endpoint = <&panel_dcp_in>;
> +                    };
> +                };
> +            };
> +
> +            dsi@0 {
> +                reg = <0>;
> +                #address-cells = <1>;
> +                #size-cells = <0>;
> +
> +                panel@0 {
> +                    compatible = "novatek,nt37801";
> +                    reg = <0>;
> +
> +                    vddio-supply = <&vreg_l12b_1p8>;
> +                    vci-supply = <&vreg_l13b_3p0>;
> +                    vdd-supply = <&display_panel_vdd>;
> +                    reset-gpios = <&tlmm 210 GPIO_ACTIVE_LOW>;
> +
> +                    port {
> +                        panel_dcp_in: endpoint {
> +                            remote-endpoint = <&dcp_intf0_out>;
> +                        };
> +                    };
> +                };
> +            };
> +        };
> +    };
> 
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry